GMT SYSTEM LEVEL PRELIMINARY DESIGN REVIEW December 17, 2013
High Level Science Goals, Key Science Requirements, Operational Concept Section 2
GMT SYSTEM LEVEL PRELIMINARY DESIGN REVIEW December 17, 2013
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HIGH LEVEL SCIENCE GOALS, KEY SCIENCE REQS, OPERATIONAL CONCEPT 2–2 GMT SYSTEM LEVEL PRELIMINARY DESIGN REVIEW December 17, 2013
Table of Contents 2 HIGH LEVEL SCIENCE GOALS, KEY SCIENCE REQUIREMENTS, OPERATIONS CONCEPT ...... 5 2.1 High Level Science Goals ...... 5 2.1.1 Discovery Space Opened Up by the GMT ...... 5 2.1.2 Contemporary Science Goals ...... 7 2.1.2.1 Formation and Evolution of Planetary Systems ...... 7 2.1.2.2 Stellar Populations and Chemical Evolution ...... 14 2.1.2.3 Galaxy Assembly and Evolution ...... 18 2.1.2.4 Dark Matter, Dark Energy, and Fundamental Physics ...... 25 2.1.2.5 First Light and Reionization ...... 28 2.1.2.6 Transient Phenomena ...... 33 2.1.3 Scientific Synergies with Other Major Facilities ...... 38 2.1.3.1 Synergy with Ground-Based Facilities ...... 39 2.1.3.2 Synergy with Space-Based Missions ...... 41 2.1.4 Summary of High Level Science Goals ...... 42 2.2 Top-Level Science Requirements ...... 43 2.2.1 Mapping Science Goals and GMT Requirements ...... 43 2.2.2 Telescope and Subsystem Requirements ...... 47 2.2.2.1 General Requirements ...... 47 2.2.2.2 Spectral Range ...... 47 2.2.2.3 Seeing-Limited Image Quality ...... 47 2.2.2.4 Motion Control ...... 48 2.2.2.5 Adaptive Optics Requirements ...... 48 2.2.2.6 Instrument Requirements...... 50 2.3 Operational Concept ...... 50 2.3.1 Organization ...... 50 2.3.2 Facilities and Infrastructure ...... 51 2.3.2.1 Summit Facilities ...... 52 2.3.2.2 Operations Center ...... 52 2.3.2.3 Science Operations ...... 53 2.3.3 Operating Modes ...... 53 2.3.3.1 Investigator Directed - On-Site (“Classical”) ...... 53 2.3.3.2 Investigator Directed – Remote ...... 53 2.3.3.3 Service Observing ...... 54 2.3.3.4 Queue Scheduled Service Observing ...... 54 2.3.3.5 Survey and Campaign Modes ...... 54 2.3.3.6 Interrupt Mode / Target of Opportunity ...... 55 2.3.3.7 GMTO Support for Operational Modes ...... 55 2.3.4 Observing Modes ...... 55 2.3.5 Time Allocation ...... 56 2.3.5.1 Engineering Time ...... 56 2.3.5.2 Contributors and Others’ Observing Time ...... 56 2.3.5.3 Director’s Discretionary Time ...... 57 2.3.5.4 Time Allocation Process...... 57 2.3.6 User Support ...... 58 2.3.6.1 Observing Assistance ...... 58 2.3.6.2 Instrument Handbooks ...... 58 2.3.6.3 Data Reduction Pipelines ...... 58 2.3.6.4 Quick-Look Reduction and Analysis Tools ...... 59
HIGH LEVEL SCIENCE GOALS, KEY SCIENCE REQS, OPERATIONAL CONCEPT 2–3 GMT SYSTEM LEVEL PRELIMINARY DESIGN REVIEW December 17, 2013
2.3.7 Instrumentation and Adaptive Optics ...... 59 2.3.7.1 Multiple Instruments and AO Available...... 59 2.3.7.2 Configuration ...... 60 2.3.7.3 Calibrations ...... 60 2.3.7.4 Performance Monitoring...... 60 2.3.8 Performance and Success Metrics ...... 60 2.3.9 Science Data Management ...... 61 2.3.10 Data Archive and Distribution ...... 61 2.3.10.1 Common Data Formats ...... 61 2.3.10.2 Data Compatibility ...... 62 2.3.10.3 Remote Networking ...... 62 2.3.10.4 Engineering Data Management ...... 62 2.3.10.5 Workstations ...... 62 2.3.11 Environment ...... 62 2.3.11.1 Environmental Data Gathering and Statistics ...... 62 References ...... 64
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2 HIGH LEVEL SCIENCE GOALS, KEY SCIENCE REQUIREMENTS, OPERATIONS CONCEPT 2.1 High Level Science Goals The GMT science case is structured in three parts: new discovery space opened by the GMT (Section 2.1.1) contemporary science goals that will be addressed by the GMT (Section 2.1.2) and scientific synergies with existing and planned facilities (Section 2.1.3). The most important aspects of the science case for this review document are those that drive requirements for the facility, scientific instruments, and operations.
The discussion begins with the new discovery space opened by increased angular resolution and the large primary collecting area of the GMT. The bulk of the discussion that follows details how the GMT can be used to address contemporary problems in astronomy and astrophysics. This is naturally where the bulk of the effort in developing the scientific requirements for the facility is focused. Since the precise mix of questions of interest at the time of first light with GMT will surely differ from what is outlined here, the discussion is focused at a level such that the derived requirements will be robust against changes in the details of the scientific questions.
2.1.1 Discovery Space Opened Up by the GMT The gain from an increased aperture in seeing-limited applications is easily characterized. The number of photons collected per unit time increases as the collecting area, or D2. Thus the signal to noise per unit time increases as the first power of the diameter in background- and source-limited applications, and as the square for detector-limited and other fixed-noise environments. The time needed to reach a given signal-to-noise ratio for a fixed flux, often called the “sensitivity”, decreases as the first or second power of the diameter in the background or detector-noise limited regimes, respectively. Many science applications with large telescopes are sky or background- limited. High-dispersion spectroscopy is occasionally detector-noise limited, while high signal-to- noise high-resolution spectroscopy of bright targets is often source-noise limited.
Adaptive optics (AO) allows one to concentrate the light from point or compact sources against the foreground sky. This improved image concentration provides additional gains in sensitivity as a function of aperture size. In the sky- or background-limited regime, the signal to noise ratio for a point source per unit time increases as D2, while the time needed to reach a given signal to noise ratio decreases as D4. The slightly dilute pupil provided by the GMT makes this scaling somewhat 4 more complex. Two of the powers of D in the D argument arise from increased collecting area; the other two arise from improved image concentration due to diffraction. The effective diameters for collecting area and diffraction differ for the GMT. Thus, when comparing to an 8 m aperture, one 2 2 should consider the GMT AO sensitivity as scaling like (24.5/8) * (21.9/8) =70.
4 This D factor is often cited as one of the primary drivers for extremely large telescopes (ELTs). Some of the most interesting applications of adaptive optics today, however, will likely not scale as D4, as they deal with objects that are partially or fully resolved at ~100 mas resolution. Integral field spectroscopy of distant galaxies, for example, is one of the key science drivers for ELTs. While distant galaxies have a significant flux in compact structures, they also have significant flux in resolved structures at HST resolution and so one will not achieve the same gains in sensitivity 3 realized for point sources. We expect gains in speed that will scale as roughly ~D in this case.
There are regimes where ELTs will deliver gains in sensitivity that scale as a higher power of the aperture diameter. These include crowded fields and contrast-limited applications. Imaging of partially resolved stellar populations in crowded regions will benefit greatly from the increased
HIGH LEVEL SCIENCE GOALS, KEY SCIENCE REQS, OPERATIONAL CONCEPT 2–5 GMT SYSTEM LEVEL PRELIMINARY DESIGN REVIEW December 17, 2013 image concentration for point sources and the reduced crowding and confusion noise associated with the unresolved component. Imaging of exoplanets near bright stars will also benefit from increased aperture through concentration of the faint exoplanet signal, reduced PSF wings from the parent star and improved stability of the PSF. Gains as steep D6, or steeper, have been posited for such application.
Figure 2-1. Discovery space opened by gains in sensitivity. We compare the 5σ depths in an hour of integration for current 8-meter apertures (tops of bars) with the depths that will be achieved by the GMT (bottoms of bars) across its entire operating wavelength range. Seeing-limited applications are shown in blue, while AO applications are shown in red. Spectroscopic limits are indicated by the curves in the visible and near-IR. Sensitivities are shown as micro-Janskys (Left) and AB magnitudes (Right).
Figure 2-1 illustrates the discovery space opened by the GMT in terms of gains in sensitivity. In this context, sensitivity refers to the depth achieved at a fixed signal-to-noise ratio in a fixed time as a function of wavelength. Figure 2-2 illustrates the discovery space opened by the increased angular resolution offered by the GMT compared to current generations of telescopes.
Figure 2-2. Angular resolution discovery space opened by the GMT using AO. The red bar shows the difference between the angular resolution of 8 m diffraction-limited AO systems and the GMT AO system, as defined by the Rayleigh criterion. We also show lines for 3 and 5 λ/D for contrast limited AO applications. The linear scale corresponding to the angular scale on the left is shown on the right for distances appropriate to exoplanets (100 pc) and distant galaxies (z=1) in AU and kiloparsecs, respectively. Seeing-limited and ground-layer adaptive optics resolutions do not scale with aperture and are shown as blue lines for reference.
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Adaptive optics also opens up a discovery space in spatial resolution (Figure 2-2). The gains in angular resolution scale as the diameter of the aperture. The factor of 3 increase in resolution compared to an 8 m aperture opens up a number of interesting areas of parameter space. The GMT will dramatically increase the volume of space over which one can image the sphere of influence for massive black holes. Similarly, the mass range that one can probe for central black holes in nearby galaxies is improved. In the case of exoplanet imaging, a factor of 3 reduction in the inner working angle opens up a large number of radial velocity detected planetary systems for imaging in reflected light, where very few are within reach today. Similarly, in the case of thermal emission, the improved angular resolution will allow the GMT to reach to stellar nurseries in the southern Milky Way and to probe terrestrial zones in nearby stars and protoplanetary and debris disks.
2.1.2 Contemporary Science Goals The following sections deal with contemporary science topics that are both of interest and are relevant to the ELT user community. The topics covered are:
• Formation and Evolution of Planetary Systems • Stellar Populations and Chemical Evolution • Galaxy Assembly and Evolution • Dark Matter, Dark Energy, and Fundamental Physics • First Light and Reionization
Each section focuses on a small number of topics of interest to illustrate where the GMT can have a high impact. Examples include using its great collecting area to probe abundance patterns in the most metal poor stars, using its increased angular resolution and sensitivity to measure dynamical masses of young galaxies, and using its sensitive near-IR spectroscopy to detect Lyα and HeII emission from galaxies in the first few hundred million years after the Big Bang.
2.1.2.1 Formation and Evolution of Planetary Systems Two paradigms currently dominate planetary formation models: core accretion (see e.g., Ida & Lin 2004 and references therein)1 and gravitational disk instability (e.g., Boss 1997)2. The former involves the collisions and sticking of rock-ice planetesimals, which grow to Earth-size and beyond; the latter posits that planets form through gravitational instabilities in the proto-planetary disk. Observations currently favor the core accretion model for inner regions, and the instability model at larger separations (i.e., >5 AU). Many current questions about planet formation will likely remain the targets of active research for a decade or more. These include: • In which environments do the core accretion and/or disk fragmentation mechanisms dominate? • To what extent are the planetary properties we observe a result of formation processes, as opposed to migration and dynamical evolution? • How do formation mechanisms impact the composition and structure of exoplanets and their atmospheres? • What is the full range of planetary system multiplicities and structures (i.e., the range of system architectures) produced? • How common are Earth-analogue planets and how often are they hospitable to life?
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Known planets today have masses that range from a few to a few thousand Earth masses, and locations that range from a few hundredths of an AU to ~100 AU from their parent stars. Understanding how this panoply of systems formed is one of the great challenges facing astrophysics. Constraining models for the distribution of planetary orbits and masses requires better statistics on the locations and timescales of planet formation, planetary migration rates, and disk dissipation times.
Kepler has identified thousands of candidate transiting planets (Borucki et al., 2011)3 and our understanding of the statistical properties of planetary systems has been greatly expanded. Kepler has revealed that Earth-sized planets in the habitable zone are common around solar type stars (Howard et al., 20114 ; Petigura et al. 20135).
Direct imaging techniques are producing their first exoplanetary detections (Marois et al., 20086, 20107; Kalas et al., 20088) and over the next decade these methods promise to find more giant planets in the outer regions of planetary systems. We can also expect that over the next 10 years, Doppler planet searches will continue to push their precision limits to lower masses, identifying terrestrial-mass planets with orbits of under a year (e.g., Howard et al., 20109, Wittenmyer et al., 2011b10), while also determining the frequency with which Jupiter-mass planets orbit Sun-like stars in orbits comparable to those of gas giants in our Solar System (e.g., Wittenmyer et al., 2011a11).
The GMT will possess multiple capabilities critical for breakthroughs in exoplanetary science. Its huge aperture will enable acquisition of spectra of transiting planets 7.5 times faster than current 8.m telescopes, enabling a new generation of spectroscopic studies of exoplanet atmospheres in the short windows allowed by primary- and secondary-transit durations. The GMT’s 24.5 m effective diameter will allow it to achieve unprecedented spatial resolution. The potential for synergy when these capabilities are combined in one facility will be powerful. For example, while transit observations and spectroscopy with G-CLEF will identify and measure the masses of habitable planets, the GMT spectrographs will study their atmospheres, and near-IR imagers will be able to image the outer planets directly.
This section addresses key questions in planet formation and evolution for which it is believed the GMT will make major contributions. These include: (1) the disk-planet connection, (2) characterization of exoplanet atmospheres, (3) probing the architecture of planetary systems through imaging and precision Doppler measurements, and (4) characterizing habitable worlds. The GMT Science Book12 also discusses the role of the GMT in advancing our understanding young stars, their jets, transport of volatiles within disks, and studies of our own solar system.
2.1.2.1.1 Young Stars and the Disk-Planet Connection Stars form and evolve hand-in-hand with planets, and stellar properties such as mass, rotation, and magnetic field strength control their co-evolution. Star formation begins with molecular clouds where discrete clumps of gas and dust gravitationally collapse to form protostars. Conservation of angular momentum during the collapse results in gas and dust settling into circumstellar and protoplanetary disks, in which planets may coalesce and grow (Williams & Cieza, 2011)13.
Obscuration and shadowing by disks put a large fraction of protostars in dark clouds beyond the reach of 8 m telescopes. It is widely thought that embedded stars are younger on average than their unobscured counterparts in the same regions, but this paradigm has yet to be tested. Winds, driven by X-ray and UV radiation ultimately limit the time available for forming planets around young stars. The GMT’s high spatial and spectral resolution capabilities will enable multiple, simultaneous astrophysical measurements that address the key issues of obscuration, age, winds and magnetic fields.
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Figure 2-3. The spectrum of a young planet such as β Pic b can reveal the composition of the atmosphere and the presence of dusty clouds. The black bars show a simulated GMT/GMTNIRS spectrum for a 1800 K planet observed around β Pic in 1 hour at a spectral resolution of 30,000, as it would look if the atmosphere were cloudless (dark blue curve) or cloudy (light blue curve). Models courtesy of Travis Barman.
Disks with masses sufficient to form a planetary system like the Solar System have been detected around more than 80% of Sun-like stars at young ages (~1 Myr) but are essentially non-existent for stars older than 10 Myr (Strom et al., 198914, Williams & Cieza, 2011). Only a few tens of these disks have been spatially resolved, largely due to the high contrast between protostars and disks, and the great distances to the stars.
If planets form early by gravitational instability (rather than by core accretion) the GMT will be able to image them around very young stars and subsequently study their orbits and atmospheres. For example, the recently detected 8 MJup planet around the 12 Myr old star β Pic has an L-band apparent magnitude of 11. Figure 2-3 shows that the GMT would easily obtain spectra of this planet in under one hour. GMTNIRS’ high-spectral resolution will enable the determination of the molecular composition of the planet, including the abundances of important molecules such as water, methane and carbon monoxide, as well as evidence for auroral emission due to a planetary magnetic field producing H3+. As more planets of lower masses and fainter magnitudes are discovered closer to their stars by direct imaging at smaller separations, GMT spectra will facilitate further studies of their physical conditions.
Studying young disks requires high spatial and spectral resolution. The GMT’s smaller inner working angle compared to 8–10 m apertures will allow it to carry out observations that probe to 2.AU at 1.6 μm or 4 AU at 3.8 μm (for the typical 140 pc distance of nearby star forming regions) thereby discovering large samples of young disks. High contrast (10-6) AO images with ~4 AU resolution will enable the first direct views of the terrestrial and gas giant formation zones in disks around the youngest nearby stars. Thermal infrared imaging at ~10 μm may further reveal temperature and structure perturbations in disks, as in Figure 2-4 and Figure 2-5. Gravitational instability leads to the formation of spiral arms that may be observable in scattered light. These features can change on short timescales (<10 years) and reveal the presence of forming planets.
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Figure 2-4. Simulated GMT image of protoplanetary disk inclined at 45 degrees to our line of sight, with a 30 MEarth planet at 10 AU that carves a gap in the disk. The left panel shows the model. The right panel shows the disk around a star at 100 pc as imaged at 3.8 µm with the GMT mid-IR imager concept, TIGER. The GMT has the power to reveal planets in formation and their interactions with the disk from which they form.
Figure 2-5. Simulated GMT image of the disk around HR4796A at 3.8 μm. Left: The Kuiper Belt-like disk at 1’’ (73 AU) has been imaged at 5x lower spatial resolution with HST, but will be revealed spectacularly by the GMT. Modeled here as smooth, the GMT would be able to reveal any clumps or asymmetries not visible from HST. Right: A close-up of a simulated TIGER image of a hypothetical inner disk–a model of zodiacal- like emission 1500x the Solar System Zodi sitting in the habitable zone of the star. The GMT would not only detect such dust but also spatially resolve it. The true distribution of dust around this star depends on the architecture of its planetary system, which could be inferred from GMT images even if the planets are too small to detect directly.
GMT observations of the CO fundamental lines will probe the kinematics of warm gas and may allow separate observations of the Keplerian gas motion, and hence a direct constraint on the stellar mass and radial motions of gas such as streamlines past a giant planet in formation.
2.1.2.1.2 Probing Exoplanet Atmospheres Observing primary and secondary eclipses of transiting planets yields insights into their atmospheric compositions that cannot be obtained with other techniques. During primary transit, when the planet crosses the stellar disc, spectroscopic observations of the depth of the transit can be used to determine the planet’s radius at a variety of wavelengths, and subsequently the properties of the transiting planet’s atmosphere (Figure 2-6). The key factor presently limiting such work is the difficulty in obtaining a high enough S/N ratio during short (typically ~1 h) transit durations. The GMT’s aperture will make it possible to achieve the required sensitivity during transits. It will also
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make it possible to use this technique on smaller planets with thinner atmospheres, thus opening the door for probing the atmospheres of the potentially habitable planets that will be discovered by missions like TESS over the coming decade.
Figure 2-6. Primary transit spectroscopy from the VLT has been used to probe the atmosphere of the 6 15 MEarth planet GJ1214b (Bean et al., 2011)
In secondary transit, when a planet passes behind the star, observations of the stellar light can be subtracted from the Planet+Star observations (obtained out of transit) revealing a planetary emission/reflection spectrum. The keys to these observations are high precision and high stability -3 near-IR spectroscopy sufficient to measure contrast levels of Fplanet/Fstar<5x10 .
Near-IR spectroscopy during secondary transits will provide unique new data on the atmospheres and compositions of eclipsing gas- and ice-giant planets. Line ratios and line shapes, particularly for molecular bands of CO and CH4, can reveal not only dayside temperatures, but also information about atmospheric pressures, temperatures, and chemical abundance profiles. Such data will yield valuable information about the formation locations of these planets, while also helping us to understand global circulation between the day and night sides in tidally locked systems.
2.1.2.1.3 Imaging Exoplanetary Systems Exoplanet direct imaging will provide otherwise unobtainable data on the formation, evolution, and multiplicity of exoplanets in wide orbits (i.e., 5–50 AU), critically complementing Doppler and transit observations, which are inherently more sensitive at smaller orbital separations. Targets for direct imaging fall into a few distinct classes: (1) planets still embedded in their parent disks, (2) young gas giants that are intrinsically bright in the near-infrared and (3) older (>1 Gyr) planets detectable via their thermal infrared emission or reflected light (Figure 2-7). The GMT will provide high contrast, high resolution imaging capabilities in the near and mid-infrared enabling the detection of exoplanets in each of these categories.
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Figure 2-7. The multiple planet system orbiting HR8799 has been resolved by multiple ground-based AO systems, including these 1.6 and 3.3 micron images taken with the LBT (Skemer et al. 201216). 2.1.2.1.3.1 Young Gas Giant Planets The L’-band is likely to be the most sensitive window for imaging giant planets. In this band, the GMT will have a resolution limit (2 λ/D) corresponding to 46 mas, and in a 1-hour observation will be able to reach a sensitivity limit of 20th magnitude. In Table 2-1 we list some representative limiting masses for GMT observations of exoplanets with ages ranging from 10 Myr to 1 Gyr. In Figure 2-8 we show simulated GMT observation of planets in the β Pic system (already known to host one 10 MJup planet). A design reference survey to L’=20 for some 50 nearby stars with a median age of 0.5 Gyr would be expected to detect some 15-20 new exoplanets with separations of 1–20 AU. Follow-up photometry and low resolution spectroscopy at wavelengths between 1 and 13 μm will be particularly critical for determining atmospheric and surface properties of these planets.
Figure 2-8. Simulated GMT observations of the β Pic system (compared to current state-of-the-art VLT L’ data). GMT will not only trivially detect the known 10 MJup planet, but will be able to detect planets of Saturn mass beyond 3 AU in this system.
Table 2-1. Detectability of planets via thermal IR imaging Distance (pc) Age Separation (AU) Mass Limit 50 10 Myr 2.3 <0.5 MJ 150 10 Myr 7.0 0.5 MJ 20 0.3 Gyr 1.0 1 MJ 10 1 Gyr 0.5 1.5 MJ
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2.1.2.1.3.2 Thermal Imaging of Rocky Planets It is likely that by the time the GMT goes into operation, nearby stars hosting rocky Earth-mass planets will have been identified by transit searches (e.g., TESS) or on-going Doppler survey programs, providing a wealth of new targets for GMT direct imaging studies. The nearest stars (d<10 pc) will be prime targets for GMT direct imaging in the L’ (3.8 μm) or N (10 μm) bands. The expected angular separation of a rocky planet from its parent star with a peak flux near 10 μm is simply a function of the apparent magnitude of the star, so the most attractive stars to search are also the brightest ones in the sky.
Table 2-2 lists (for 9 of the nearest stars) the spatial separation at which a planet would maintain a “Warm Earth” temperature of 280 K, suitable for N-band detection. Planets at these separations would lie within their system’s habitable zone and be outside the GMT’s 1.5 λ/D inner working angle threshold. The N-band brightness of a 2 REarth planet at 5 pc is approximately 9 μJy, suggesting that super-Earths would be well above the expected noise level in a several hour observation.
Of course, rocky planets may exist in a range of orbits around their parent stars. While planets at larger separations would be cooler and less detectable, planets closer to their stars will have equilibrium temperatures correspondingly higher, and would be even more amenable to study. An Earth-size planet at an equilibrium temperature of T=600 K would be roughly four times closer than a true Earth analog (at 280 K) and would have a peak flux in the L-band atmospheric window. If we assume blackbody emission of the planet at its equilibrium temperature, it would have an absolute flux of 2 μJy, which compares favorably with the photometric limit of 0.5 μJy expected for a GMT limited by sky and telescope background in a 1-hour observation. While the approximation of a 600 K blackbody for a hot Earth is almost certainly inaccurate, spectral models for hot planets with a range of atmospheric compositions have been examined (Miller-Ricci et al., 2009)17. These models suggest that because the L’-band is a generally transparent window, the detection of “hot Earths” at L’ is feasible with the GMT.
Table 2-2. Potential targets for rocky planet detection with the GMT mid-IR imager TIGER
“Warm Earth” “Hot Earth” Object D (pc) 280K planets 600K planets
α Cen A 1.35 770 mas 170 mas α Cen B 1.35 450 mas 100 mas α CMa 2.64 2400 mas 520 mas ε Eri 3.22 170 mas 40 mas α CMi 3.5 490 mas 110 mas τ Cet 3.65 210 mas 50 mas α Aql 5.14 650 mas 140 mas β Hyi 7.47 280 mas 60 mas α PsA 7.69 640 mas 140 mas
The factors limiting the detectability of “warm” versus “hot” Earths are different. Photometric sensitivity in the N-band limits the number of stars around which a warm rocky planet can be detected. For L’ “hot Earth” studies, the available photometric sensitivity will, in principle, allow detection of even sub-Earth mass planets, but only for planets outside the ~1.5 λ/D separations shown in Table 2-2. The science that would come from the observation and subsequent detailed study of these classes of planets would be truly groundbreaking.
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2.1.2.1.4 Probing the Nearest Habitable Planets Using Doppler Spectroscopy (Earth Analogues Orbiting Sun-type Stars) Doppler velocity measurements will remain critical in the decade ahead, since only the combination of Doppler velocity measurements and transit searches can reveal both exoplanet mass and size. This combination delivers exoplanet bulk density, which is a critical parameter in determining whether the potentially habitable low-mass planets we find orbiting other stars are rocky, small ice- giants, or water worlds.
With its high-precision G-CLEF spectrograph, the GMT will be able to carry out a census of the population of Earth-like planets orbiting the nearest Sun-like stars. Such a census requires sub- 10_cm/sec Doppler velocity precisions at multiple epochs over a planetary orbital period. Recent Doppler detections by the HARPS spectrograph indicate that these extraordinary levels of precision are achievable. Indeed, the ability to detect planets down to a few Earth masses at periods of up to 90 d has been demonstrated by obtaining multiple observations averaged over a single night, and 40-50 epochs per year over several years (Pepe et al., 2011)18. Moreover, when those detected planets are removed from the data sequence, and the resulting residuals binned over periods of 40– 50 d, the resulting data set displays residual velocity dispersions that drop below 20 cm/sec.
This result shows that there are stars in the solar neighborhood with the intrinsic Doppler stability (at periods of interest) to detect Earth-like planets, as long as sufficient photons can be detected, and astrophysical sources of noise can be averaged over. Observations that achieve these goals can potentially detect the much sought-after habitable Earth-analogue planets in ~1 AU orbits.
Obtaining such data for a meaningful sample will require the combination of the GMT’s massive aperture and G-CLEF’s extraordinary stability and precision. The HARPS data described above for HD20794 was collected by integrating nine 4-m telescope nights over 3 years, all dedicated to this one target, delivering a ‘per night’ dispersion of 82 cm/s. Dropping this dispersion down to 10_cm/sec will require averaging over some 70 epochs to acquire the extra factor of 8.2 in signal- to-noise required. This detection is completely unfeasible on 4- or 8-m telescopes. The GMT, however, will collect photons 37 times faster than HARPS’, making it possible to study a sample of 10 Earth-analogue host stars in less than 36 nights per year over the first 5 years of operation. It bears noting that this represents the most conservative possible calculation, based only on presently achieved Doppler precision. Recent history suggests that further gains in precision are likely.
2.1.2.2 Stellar Populations and Chemical Evolution Baade’s early recognition of distinct stellar populations has provided an enduring framework for studies of galaxy formation and evolution, stellar chemistry, and stellar dynamics. Today, any viable model for the formation of the Milky Way must address the origin of thin disk, thick disk, bulge and halo populations, and the diversity of their dynamical, chronometric, and chemical properties. Our understanding of stellar populations in external galaxies is still quite limited and is based largely on integrated light spectra. With its southern location and well-suited instruments, the GMT (in concert with SkyMapper, VISTA, VST, LSST, DES and other southern surveys) will open a number of avenues for detailed studies of stellar populations in the outer halo, the Local Group, and beyond.
The GMT will greatly enhance stellar science through the acquisition of high-resolution spectra of brighter targets with S/N ratios that cannot be achieved today and by probing stellar systems at larger distances than possible with 8-10 m apertures. Diffraction-limited imaging provides an additional avenue for stellar population studies with the GMT. The sections below highlight a few of the topics to be explored with the GMT in the area of stellar populations and chemical evolution.
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2.1.2.2.1 Characterizing the Most Metal-Poor Stars Extremely metal-poor stars ([Fe/H] < –3.0) predate the main halo population, possibly from a pre- Galactic era. Some stars are so metal-poor and have such unusual compositions that they are thought to reflect the composition of individual supernova events after the Big Bang (e.g., McWilliam, 199519; Beers & Christlieb, 200520; Frebel, 201021). These objects are profoundly important for understanding the very first chemical enrichment in the Universe, and provide important constraints on the nature of Population III stars, their IMF, and the yields of the first massive core-collapse supernovae. Unfortunately, since these stars are so metal-poor, (the most metal-poor stars currently known have [Fe/H]~ -5.5), the strongest absorption lines of the most important elements will be too weak to measure in normal high dispersion spectra with S/N~100 (Frebel et al., 200522, Aoki et al., 200623).
Figure 2-9 shows the spectrum of the extremely metal-poor warm subgiant HE1327-2326, which has Teff ~6200 K and [Fe/H]= -5.4. Also shown, for comparison, is the spectrum of extremely metal-poor turnoff star, G64-12 for which [Fe/H]= -3.2. The region around the strongest Fe line is displayed and its equivalent width is only ~7 mÅ in the HE1327-2326 spectrum. If this object had been somewhat hotter or somewhat more iron deficient, no Fe line could have been measured with current facilities. Given the odd chemical abundance pattern of extremely high [C, N, O/Fe] element ratios and elevated [alpha/Fe] found in both of the currently known [Fe/H]< -5.0 stars, accurate measurements of the Fe abundance from several extremely weak Fe lines are crucial.
Figure 2-9. Spectral region around the strongest Fe line in the optical wavelength regime at 3860 Å. It illustrates the effect of metallicity on line strengths for the Sun and three additional stars with decreasing metallicity. Compared to G64-12 (2nd from bottom), this line in HE 1327-2326 (bottom), with [Fe/H] = -5.4, is hardly detectable. Figure from Frebel & Norris (2012)24.
The next generation of photometric and spectroscopic surveys will unveil large samples of extremely metal poor stars. The SkyMapper Southern Sky Survey (Keller et al., 200725), for example, expects to provide a 100-fold increase in the numbers of [Fe/H]< -3 stars, as well as up to 50 objects with [Fe/H]< -5.0. Most of these stars, however, will be too faint for high resolution spectroscopy with current facilities. Only with the light-collecting power of an ELT such as the GMT will it be possible to study these fossil stars with the required precision to generate a much- improved understanding of the early Universe and the processes governing nucleosynthesis.
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The GMT could make major contributions to stellar archaeology through a two-component observing program. A discovery mode (R~20,000, S/N~30 at 4000 Å) would be used to confirm the metallicity of pre-selected targets from large surveys and to quickly identify any unusual abundance characteristics (e.g., ultra-metal-poor, or r-process enhancement). Important targets would then be observed with a resolution of R~40,000 and S/N~100 to acquire data required for a detailed chemical abundance analysis.
In a modest allocation of nights over 2-3 years, one could survey several hundred stars to V~18, selecting a sample of a few tens of stars for detailed abundance work. Over the course of a few years, a modest sized group working within the GMT community could then extract a great deal of value-added science from the large-scale photometric and spectroscopic survey programs planned for the coming decade. In particular, such studies would permit a much more accurate definition of the metallicity distribution function (MDF) at the lowest metallicities. The MDF is currently poorly defined as the number of known extremely metal-poor stars is small: for example, at the present time there are only a handful of stars known with [Fe/H] < -4.0. Characterizing the extremely metal-poor tail of the MDF is, however, pivotal for constraining both models of the formation of the first stars and the role of processes such as SNe feedback in the earliest stages of galaxy formation (e.g., Salvadori et al., 2007)26.
Such studies will also play a vital part in defining the role of carbon abundances at the lowest metallicities. Approximately 20% of stars with [Fe/H] ~ -2 are significantly enhanced (by a factor of ~10 or more) in carbon relative to the scaled solar value, and this percentage rises to ~100% at the lowest abundances. Carbon is probably the first element to enter the ISM and is therefore likely to be a major driver of dust formation at the earliest epochs. Yet the origin of the substantial carbon enhancements at the lowest metallicities is not well understood, as there are potentially a number of production mechanisms involving stars of different mass. Nevertheless, with detailed abundance studies of a large sample of extremely metal-poor stars, we can expect to untangle the role of carbon enhancements and thus advance our understanding of the physical processes that govern star formation at the earliest times.
2.1.2.2.2 Age Dating the Oldest Stars The ages of the oldest stars can be directly determined by measuring the abundances of long-lived radioactive isotopes such as 232Th (half-life 14 Gyr) and 238U (4.5 Gyr). Specifically, the age of a star can be derived by comparing the abundances of Thorium (Th) and/or U with those of stable r- process nuclei, such as Europium (Eu). While Th is often detectable in metal-poor stars that are enhanced with r-process elements, determining U abundances is particularly challenging because the only U line in the optical and near-IR spectral region with sufficient strength to permit abundance determinations is extremely weak and lies in the UV-blue spectral region (~3860 Å) where there are many other contaminating lines from more abundant species.
Currently, 238U has only been detected in three stars, and one of these detections is tentative. For HE1523-0901 (V=11.1) and CS 31082−001 (V=11.3), high-resolution spectra with R~80,000 and S/N~350-500 at 4000 Å were required to successfully measure the optical U line from which the abundance was deduced (Frebel et al., 2007). The spectral region around the U line in these stars is shown in Figure 2-10. HE1523-0901 was determined to have an age of 13.2 Gyr by averaging the results of several nucleochronometers involving combinations of Eu, Os, Ir, Th and U (Frebel et al., 2007), while for CS31082-001, the U/Th chronometer yielded an age of ~14 Gyr (Cayrel et al., 2001)27. These ages provide a lower limit to the age of the Galaxy and hence, the Universe. They are consistent with the age of 13.75 Gyr derived from cosmological parameters measured in the WMAP experiment (Larson et al., 2011)28.
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Figure 2-10. Spectral region around the only available uranium line in HE1523-0901, the r-process enhanced star with the strongest overabundance in heavy neutron-capture elements in comparison to CS31082-001, the only other star with a U detection (but 200 K cooler than HE1523-0901, resulting in a significantly weaker U line). A larger region is shown on the left, with a zoom-in version of the right (Frebel et al., 2007)29.
The stars most suitable for direct age determinations are cool metal-poor giants that exhibit strong overabundances of the r-process elements. Unfortunately, such stars are often also very Carbon- rich and the 238U line is blended and not measureable. For example, in the extreme r-process star CS22892-052, only the Th/Eu ratio could be employed yielding an age of ~14 Gyr (Sneden et al., 2003)30. Compared to Th/Eu, the U/Th ratio is much more robust, however, with respect to uncertainties in the theoretically derived production ratio, as a result of the similar atomic masses of Th and U (Schatz et al., 2002)31. Hence, old metal-poor stars displaying both Th and U are the most valuable for nucleochronometric age determinations. Candidates for further study will come from large area surveys of very metal-poor stars such as SEGUE, SkyMapper and HERMES.
With the GMT’s optical high resolution spectrograph it will be possible to obtain spectra of stars suitable for nucleochronometric age determinations with S/N of 500 or more in just a few hours. This S/N and a resolution of R>50,000 are required to detect and adequately measure the weak U line. Spectra of this quality will also enable the detection of weak lines of a number of other rarely studied elements permitting a full chemical characterization of the r-process element enhanced metal-poor stars. For example, Lead (Pb) measurements in these stars (Pb being the decay product of Th and U) are even more challenging (S/N>500 required), but they will provide the ultimate empirical constraint for r-process modeling and thus nuclear astrophysics. Ultimately, a large stellar database with measurements of the heaviest chemical elements will not only provide a constraint on cosmological models but will also further our understanding of the production of the heavy elements in the Universe.
2.1.2.2.3 Globular Clusters in Local Group Galaxies and Beyond With its large collecting area and high angular resolution in the diffraction-limited mode, the GMT will be able to uniquely contribute to our understanding of dense stellar systems. Globular clusters in Local Group galaxies and other close neighbors can be studied in great detail with the GMT, while integrated light studies can probe the dynamics and abundances in globular cluster systems associated with large galaxies and high stellar densities in the Virgo and Coma Clusters.
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Figure 2-11. Simulated images of a globular cluster at the distance of Centaurus A (3.8 Mpc). The cluster has a core radius of 3 pc and the field shown corresponds to 2” on a side. The three panels show the cluster as imaged with PSFs appropriate to HST, Gemini and GMT at 1.5 µm. The GMT simulation uses a PSF with a Strehl ratio of 0.7.
Figure 2-11 shows a simple graphical simulation of diffraction-limited images of a globular cluster with a core radius of 3 pc at the distance of Centaurus A (NGC 5128). The three panels show the cluster as imaged with Hubble, a diffraction-limited 8 m, and the GMT using the LTAO adaptive optics mode. The reduction in crowding noise is dramatic and illustrates one of the strengths of the ELTs–their ability to access crowded environments beyond the reach of Hubble, current ground- based telescopes, and the James Webb Space Telescope.
Color-magnitude diagram studies based on near-IR imaging with LTAO have the potential to provide much new information on the ages (via the luminosities of thermally pulsing AGB stars) and metallicities (via red giant branch colors) for both the star clusters and the field-star populations in many galaxies within the local Universe (D<10–15 Mpc). Due to the large diversity of galaxy types in this volume compared to the Local Group (e.g., the S0 type Sombrero Galaxy, and the E type Centaurus A), the results will provide broader constraints on galaxy formation than are currently available.
2.1.2.3 Galaxy Assembly and Evolution Understanding the formation and evolution of galaxies remains a key challenge in astrophysics. Sophisticated theories and numerical modeling now allow for highly refined models to be directly compared to observations, leading to a deeper understanding of the physical processes that drive galaxy assembly and evolution. Hierarchical cold- and hot-flow accretion, mergers involving dissipation (gas-rich or “wet”) or dissipationless (gas-poor or “dry”) mergers, feedback and outflows, and rapid monolithic aggregation are paradigms that are under tension in contemporary theoretical frameworks for understanding the early formation, structural properties, and evolution of luminous galaxies.
The GMT will make unique contributions to our understanding of the formation and evolution of galaxies through its ability to obtain spectra of extremely faint objects and to image galaxies with spatial resolution on the order of 100 pc at large cosmological distances. Large surveys of the present-day galaxy population provide a firm benchmark for evolutionary studies, and sample the population of low-mass dwarfs, while deep survey fields from NASA’s Great Observatories provide sizable samples of galaxies at large and intermediate redshifts. Future space- and ground- based facilities will have strong synergy with the GMT in this science area, either by providing survey databases or by accessing regions of the resolution-wavelength space not probed by the GMT.
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2.1.2.3.1 Near-Field Studies of Galaxy Assembly Dwarf galaxies, and ultra-low-mass dwarfs in particular, provide a unique laboratory for studying the building blocks of today’s galaxies. The lowest mass systems present today are believed to be relics of early dark matter halos that have avoided merging into larger systems. These heavily dark-matter dominated systems provide a unique opportunity to study the small-scale properties of dark matter halos and to test the CDM paradigm (Simon & Geha 200732; Geha et al., 200833).
The number of known ultra-low mass systems has grown rapidly with the advent of large sky surveys (e.g., Willman et al., 200534; McConnachie et al., 200835). Future surveys, and LSST in particular, will greatly increase the available volume for dwarf-galaxy studies. In the near-term, SkyMapper and the Dark Energy Survey (DES) will open the southern sky to dwarf galaxies to depths greater than those of SDSS in the north and the equatorial survey strip.
The shallow potential wells in ultra-low mass dwarfs make them unique environments for studying the enrichment process. Single supernovae events can leave a clear imprint in the abundance patterns of subsequent stars. The number of stars accessible to detailed abundance work is presently frustratingly small, as Figure 2-12 illustrates. The visible and near-IR echelle spectrographs being developed for the GMT are particularly well-suited to this science, and the facility multi-fiber system (MANIFEST) could greatly increase the power of the visible echelle in studying the dark matter content and stellar populations in low-mass systems.
Figure 2-12. CM diagrams for known dwarf and ultralow mass dwarf galaxies. The current limit for a few hours of integration on an 8 m telescope is shown by the red line. The dashed blue line is the analogous limit for the GMT using the G-CLEF fiber fed echelle spectrograph; the green shows the sensitivity with only 4 primary mirror segments. The number of stars within reach of velocity and abundance determinations is greatly improved and some systems that are beyond the reach of 8 m Echelle spectrographs (e.g., CVn I, Leo IV) will be accessible for the first time with the GMT. Even in the 4-mirror configuration, many more stars are accessible, although we cannot reach the red clump stars in Sculptor or Sextans until the primary mirror array is fully populated. (J. Simon, priv. comm.).
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Figure 2-12 shows color-magnitude diagrams for dwarf galaxies ranging from fairly rich systems (such as Fornax) to those with only a handful of constituent stars (such as Segue 1). The reach of current echelle spectrographs is marked by a fiducial line at V=19. The GMT and the G-CLEF echelle will allow one to reach ~1.5 magnitudes fainter, greatly increasing the number of accessible stars, particularly for the lowest mass dwarfs. Some systems that are beyond the reach of 8 m echelle spectrographs (e.g., CVn I, Leo IV) will be accessible for the first time with the GMT. 2.1.2.3.2 The Galaxy Building Epoch The process of galaxy building spanned several Gyr, with the peak period of mass growth occurring between redshifts of ~5 to as low as ~0.5, with the bulk of the mass growth in M* galaxies occurring in the interval from 1 Figure 2-13. Comparisons between state-of-the-art spectra of red galaxies with simulated spectra from NIRMOS on GMT. The left panels show Gemini/GNIRS spectra and VLT/XShooter spectra of red galaxies with J=22.5 and 19.9, respectively. HIGH LEVEL SCIENCE GOALS, KEY SCIENCE REQS, OPERATIONAL CONCEPT 2–20 GMT SYSTEM LEVEL PRELIMINARY DESIGN REVIEW December 17, 2013 A broad range of processes contribute to the growth of galaxies: conversion of in-situ gas into stars, accretion of outside gas through cold flows, and the build-up of stars and gas through major and minor galaxy mergers. These processes are modulated by feedback from massive stars and supernovae, large-scale galactic winds, and outflows powered by nuclear AGN. Understanding the interplay between these various processes and their impact on the present-day properties of galaxies is one of the most active areas of research today. 2.1.2.3.2.1 Dynamical Masses Theoretical treatments of the growth of structure on galactic scales and greater deal primarily with total rather than baryonic masses. The underlying dark matter distribution drives the growth of galaxies, groups, and clusters through accretion of gas along dark matter filaments, and through hierarchical merging of structures in over-dense regions. Comparison between theory and observation is greatly facilitated by accurate determinations of the dynamical masses for galaxies, groups, and clusters. Several methods are employed to acquire dynamical masses for galaxies at z>1. Determining dynamical masses from stellar velocity dispersion measurements is best achieved in the near-IR (where spectroscopy is sensitive to stellar absorption features in the rest- frame optical at redshifts 1.5 The expected velocity dispersions in passively evolving galaxies selected in near-IR multi-color surveys are expected to be in the 100–500 km/sec range. Very long exposures with IR spectrometers on 8 m telescopes have led to reports of ~500 km/sec dispersions in luminous red galaxies at z~2 (van de Sand et al., 201136), as shown in Figure 2-13. The GMT’s large collecting area coupled with an R~3000-5000 near-IR spectrograph will allow velocity dispersion measurements with high confidence in massive galaxies, and will enable one to observe L* and sub-L* systems at z~2. Figure 2-13 compares a 29-hour Gemini/GNIRS spectrum with a simulated 3-hour observation with GMT/NIRMOS. 2.1.2.3.2.2 Kinematics of Star-Forming Galaxies Galaxies at the peak of the galaxy building era are comprised largely of “clump-cluster” sources and their edge-on counterparts, “chain galaxies” (Elmegreen et al., 2008)37. The kinematics of these galaxies is presently being explored through two-dimensional integral field spectroscopy. These observations, using Hα or [OIII]5007, allow one to map both line-centers and line-widths over the full face of distant galaxies. While these galaxies often present projected diameters of ~2”; ten times the nominal 200 mas slit widths common to instruments such as JWST/NIRSpec or GMT/NIRMOS, they contain th substructure on scales of 20–30 mas or ~1/10 of this resolution. Adaptive optics allows one to sample many independent spatial regions across galaxies that are typically ~1-2” in size. The GMTIFS AO-fed IFU spectrograph designed for the GMT will have spaxel scales well-matched to the sizes of the high surface brightness clumps. To date, IFU observing programs on 8 m apertures have produced some surprising results. The line widths in most of the intense star forming systems are high and there is a broad range of velocity fields. Some systems show apparently well-organized rotation curves despite irregular morphologies, while others have disorganized velocity fields or multiple components indicative of ongoing mergers. Most of these observations, however, are badly photon starved. HIGH LEVEL SCIENCE GOALS, KEY SCIENCE REQS, OPERATIONAL CONCEPT 2–21 GMT SYSTEM LEVEL PRELIMINARY DESIGN REVIEW December 17, 2013 Figure 2-14. Simulated velocity channel maps from an observation of a z=1.5 galaxy with the GMTIFS instrument on the GMT. An ordered velocity field with an amplitude of +/- 200 km/sec was imposed on an ACS i-band image from the Hubble Ultra Deep Field. This simulation assumes 50 mas spatial elements and a total line flux of 1.1x10-16 erg cm-2 s-1 (Bournaud et al., 2008) which was observed over a period of 12 h (9 h on source +3 h on sky). The GMT and other ELTs will improve the photon rates at fixed spatial sampling by an order of magnitude thus allowing robust determinations of galaxy velocity fields over a range of masses and luminosities. GMTIFS will provide a gain in both surface brightness sensitivity and spatial sampling, allowing more detailed studies of high surface brightness systems and access to a broader range of surface brightness levels. Figure 2-14 shows velocity channels from a simulated GMTIFS observation of a galaxy at z=1.5. 2.1.2.3.3 Feedback and the Galaxy-IGM Connection Feedback (the injection of energy into gas in galaxies and the resulting regulation of star formation) is thought to be the key to understanding how present day massive galaxies acquired their distinctive morphologies, masses, and stellar content. The IGM and CGM (defined to be the gas within about 300 kpc of the galaxies) provide a laboratory in which the feedback effects from galaxy formation and AGN accretion can be measured. One promising route to understanding the relevant baryonic processes is to survey galaxies and gas in the IGM in the same cosmic volumes during the epoch when they were exerting the most influence on one another, near the peak star- forming and black hole accretion era at 2 The intervening absorption-line systems in (background) galaxy and QSO spectra are sensitive to low column densities and high ionization states. These provide our best constraints on the extent of cold gas in the CGM around distant galaxies. Furthermore, (rest-frame) UV spectra of distant HIGH LEVEL SCIENCE GOALS, KEY SCIENCE REQS, OPERATIONAL CONCEPT 2–22 GMT SYSTEM LEVEL PRELIMINARY DESIGN REVIEW December 17, 2013 galaxies allow for detailed study of galaxy-scale outflows and/or inflows of cold gas via strong interstellar absorption lines and Lyα emission. Current surveys using large samples of spectroscopic data for LBG galaxies at 2 Figure 2-15. Simulation of the expected data quality of a galaxy at z=5 with I=25.1 AB mag. The top panel shows a simulated spectrum of the galaxy in 1 h with Keck/DEIMOS where the S/N is ~0.5/pixel and only Lyα in emission would be detected (if present). The bottom panel shows the equivalent spectrum with 1 h on GMACS, where the predicted S/N is ~2/pixel (~5/resolution element). In this spectrum, galaxy ISM absorption lines are already visible. Large spectroscopic surveys using the GMT with GMACS, which probes a longer redshift baseline and larger range in luminosity, will greatly extend this work. Specifically, GMACS would obtain spectroscopic observations of a large sample of galaxies from z~1.5 to z~5 and beyond, spanning fully the cosmic volume when galaxies were most active. For galaxies at 2 The current expected performance of the GMT with GMACS is that it will achieve S/N=10 for sources at about 24.5 mag at R~2000 in 1 hour. At this S/N, ISM absorption features become apparent even in these fainter galaxies. Typically, redshifts for LBGs based on absorption lines require S/N~2-3 per resolution element, which is doable with GMT/GMACS in about 1 hour for galaxies with 25.1 mag and R~2000, as illustrated in Figure 2-15. Therefore, assembling a sample of galaxies to probe the gas kinematics at a single redshift (e.g., z~2) requires roughly 25 GMACS masks. This will require about 4 nights (assuming 1 hour per slit mask and an overhead factor of 1.5). Extending this survey to a range of redshifts will require a larger investment of time, but will be doable in ~20 nights on the telescope. This science requires that the optical spectrographs have HIGH LEVEL SCIENCE GOALS, KEY SCIENCE REQS, OPERATIONAL CONCEPT 2–23 GMT SYSTEM LEVEL PRELIMINARY DESIGN REVIEW December 17, 2013 sensitivity over a wide wavelength range (~0.3-1 micron) to detect the rest-frame UV spectral features of the gas associated with the ISM and CGM of galaxies for 2 2.1.2.3.4 The Galaxy-Black Hole Connection One of the most interesting discoveries in galaxy dynamics in recent years is the close connection between bulge dynamics and central black hole masses. High resolution imaging observations with HST, and spectroscopy from the ground and from orbit revealed that supermassive black holes are common in the centers of luminous galaxies. The connection between bulge velocity dispersion and central black hole mass suggests a closely-linked formation and evolutionary process (Figure 2-16). The suspected role of central black holes and AGN in feedback and quenching of star formation makes gaining a deeper understanding of the black hole-galaxy connection all the more pressing. Adaptive optics and integral field spectrographs are opening a much broader range of parameter space and survey volume to ground-based telescopes. The need to resolve the black hole sphere of influence and reach surface brightness levels characteristic of stellar bulges make observations beyond z~0.25 very challenging for 8 m telescopes. Figure 2-17 shows the angular size of the black hole sphere of influence as a function of mass. Figure 2-16. The local black hole mass-sigma relation from Gultekin et al., 200939. Objects are color coded by the Hubble type of their host galaxies. The central black hole mass correlates strongly with the bulge velocity dispersion. Exploring the extremes of this correlation is a high priority for ELTs and will allow one to discriminate between some classes of models. Even with the large gain in collecting area provided by the GMT, exposure times required to obtain accurate stellar velocity dispersions are quite long and depend on redshift and available spectral features. For redshifts below ~0.6 the CO band heads offer the best features. H-band spectra with R=5000-10000 should provide sufficient resolution to suppress the impact of atmospheric OH emission and provide enough velocity resolution for accurate mass modeling. HIGH LEVEL SCIENCE GOALS, KEY SCIENCE REQS, OPERATIONAL CONCEPT 2–24 GMT SYSTEM LEVEL PRELIMINARY DESIGN REVIEW December 17, 2013 We expect that exposure times with the GMT and an IFU at z~0.5 will be around 8 hours for a spatial sampling of 12 mas. This will Nyquist-sample the K-band PSF in the diffraction-limited mode. Using the finest scale for GMTIFS (6 mas) will likely increase the required exposure time. At z~1 the exposure times should be comparable because one can access the strong CaII triplet features in the H-band. At redshifts of z~2 stellar features become very difficult to discern due to the strong surface brightness dimming, but narrow emission lines, particularly [OIII]5007 and Hα, will be very useful velocity tracers. Figure 2-17. The angular size of the sphere of influence as a function of black hole mass. The diffraction limit of GMT in the J- and H-bands is shown by the dotted line. A well-balanced GMT survey of the evolution of the MBH-σ relation will contain a mix of galaxies at z~0.25, 0.5, and 1 with a sampling of narrow-lined AGN at z~2. Such a program can be carried out in 40-50 nights spread over a few years. 2.1.2.4 Dark Matter, Dark Energy, and Fundamental Physics Our understanding of the constituents of the Universe and the evolution of structure has improved dramatically in recent decades. This has come about through a combination of theory and multi- wavelength observations of phenomena as diverse as Cepheid variable stars, supernovae, galaxy clusters, and diffuse background radiations. Giant telescopes will continue to play a leading role in cosmological studies through their access to key diagnostics and sensitivity to objects at great distances. This section considers the GMT’s role in advancing our understanding of dark matter and dark energy through calibration of large-scale cosmological probes, dynamical studies of dark matter in massive galaxy clusters, and the structure of dark matter halos in low mass dwarf galaxies. 2.1.2.4.1 Dark Energy Probes Several ambitious projects are underway, or in the planning stages, that aim to probe the expansion history of the universe using standard rulers. Baryon Acoustic Oscillation (BAO) experiments rely on a fixed scale imprinted on the matter distribution at recombination. Determinations of the HIGH LEVEL SCIENCE GOALS, KEY SCIENCE REQS, OPERATIONAL CONCEPT 2–25 GMT SYSTEM LEVEL PRELIMINARY DESIGN REVIEW December 17, 2013 angular size of the fixed 150 Mpc co-moving scale of the oscillations at high redshifts provide a direct distance determination on cosmological scales. The distance-redshift relationship is a powerful probe of the underlying cosmology and hence, the basic cosmological parameters. Two large-scale BAO programs (LSST and the DES) rely on photometric redshifts to determine the two-point correlation function in redshift bins. Photometric redshifts can be quite precise, approaching errors of a few percent rms. These surveys must be calibrated with spectroscopic samples as they probe redshifts and luminosities beyond current training sets. Hence, there is a continuing need for spectroscopic redshift surveys that are complete to the LSST detection limit and that are large enough to sample the full range of galaxy types with good statistics. The GMT can provide these data with optical and near-IR multi-object spectrographs. Samples of 10,000– 20,000 redshifts could be assembled with a modest investment of observing time on the GMT and these could play a vital role in determining cosmological parameters from large imaging surveys. 2.1.2.4.2 Clusters and Dark Matter The distribution of mass within rich clusters of galaxies is diagnostic of the history and assembly of these large structures. The value of the cosmological parameter σ8, the normalization of the matter power spectrum to 8-Mpc scales, is exquisitely sensitive to the number of high-mass clusters of galaxies, while the rate of evolution of the cluster mass function depends powerfully on Ωm. Therefore, cluster numbers and their evolution have proved to be reliable tools for probing the world-model and key cosmological parameters. Several large cluster surveys are underway (South Pole telescope) or planned for the coming decade (e.g., EUCLID). The GMT can provide spectroscopic redshifts, velocity dispersions, and weak lensing maps–essential data for cosmological studies based on the cluster mass and redshift distributions. Figure 2-18. Example of a strong cluster lens from the SDSS survey (SDSSJ1038+4849). Four galaxies with redshifts ranging from 0.8 to 2.8 are each imaged multiple times by the rich foreground cluster. The location and shapes of the various lensed images can be used to map the distribution of dark matter in the cluster and compare it with the distribution of luminous matter. See Bayliss et al., 201140 for details. Strong lensing, illustrated in Figure 2-18, provides complementary and important information about mass distribution down to the scale of the cluster cores, while small distortions in the shapes of background galaxies (weak lensing) probes the overall mass profile. The combination of weak and HIGH LEVEL SCIENCE GOALS, KEY SCIENCE REQS, OPERATIONAL CONCEPT 2–26 GMT SYSTEM LEVEL PRELIMINARY DESIGN REVIEW December 17, 2013 strong lensing allows one to measure substructure and the concentration of the mass in the clusters, as well as the overall ellipticity of dark matter in the clusters. In at least some cases, the central concentration appears to be higher than predicted by ordinary CDM, possibly suggesting an earlier formation for these structures. Most clusters arcs are beyond the reach of spectroscopy with 8 m telescopes, but can be studied with the GMT. Samples of strong lenses will come from DES and LSST for z<1 and from Euclid for z>1. 2.1.2.4.3 Dark Matter Profiles in Dwarf Galaxies A powerful test of the properties of dark matter comes from the shape of the dark matter density distribution. Cold Dark Matter (CDM) predicts that dark matter halos should show steep central density “cusps” (Navarro, Frenk & White 199641, NFW). Dwarf galaxies are ideal test subjects to measure dark matter profiles as they are highly dark-matter dominated (with mass-to-light ratios approaching 1000). Since the baryons make a negligible contribution to the mass even in the inner regions, the dark matter dictates all kinematics. An ongoing debate centers on whether dark matter halos exhibit “cusps” or show shallow density- profile “cores”. Velocity measurements of stars in low mass dwarf galaxies allow one to derive the distribution of the dark matter (e.g., Walker et al., 2009)42. As illustrated in Figure 2-19, the current data allow for mass profiles including a cuspy NFW profile as well as a halo+core. The current limits are restricted by both the number of dwarf galaxies studied and the number of stars per galaxy for which we have accurate kinematic information. Figure 2-19. The left panel shows the mass interior to the half-light radius and the right panel shows the mean density within the half-light radius for dwarf galaxies (adapted from Walker et al., 2009). The curves show the best-fitting mass profiles, including the NFW profile with a cusp (γ = 1) and a cored model (γ = 0). Currently both dark matter mass profiles are consistent with the observations. A wide-field optical spectrograph such as GMACS/MANIFEST will provide a technological leap for measuring the kinematic properties of dwarf galaxies. Confirming that dwarf galaxies are gravitationally self-bound systems generally requires kinematic information of at least 100 stars to R~23 mag at S/N=5. Since dwarf galaxies are low mass objects, their internal velocities are small and subsequent kinematic observations require precision on the order of 3 km/s, setting an observational spectral resolution requirement of R~6000. This could be achieved on the GMT with MANIFEST feeding an echelle, such as G-CLEF, or by an echellette mode for GMACS. HIGH LEVEL SCIENCE GOALS, KEY SCIENCE REQS, OPERATIONAL CONCEPT 2–27 GMT SYSTEM LEVEL PRELIMINARY DESIGN REVIEW December 17, 2013 2.1.2.5 First Light and Reionization A small number of seminal events mark sharp and distinctive transitions in the history of the Universe: the end of inflation, the quark-Hadron phase transition, recombination, and reionization (Figure 2-20). The latter, the time when the intergalactic medium (IGM) was reionized, is intimately connected to the formation of the first massive collapsed objects and the birth of galaxies. Exploring the era when galaxies first formed has been among the forefront goals of extragalactic astronomy since the discovery of the hot Big Bang. Figure 2-20. A graphical history of the Universe (Robertson et al., 2010)43. Key events relating to the early history of the Universe–recombination, the cosmic dark ages, the birth of galaxies and reionization of the IGM are illustrated. The GMT will allow us to probe the formation of the first galaxies near the end of the dark ages. The search for the first galaxies, both from empirical and theoretical perspectives, has been underway since the 1970’s and we are now able to observe and crudely characterize galaxies in the first few hundred million years after the Big Bang. The GMT, working in conjunction with JWST, SKA and other facilities, will provide new and powerful observational tools for studies of the reionization epoch and the period of early galaxy growth that followed. In this section we illustrate a few areas in which the GMT is expected to have a significant impact and highlight ways that GMT instruments and other facilities can work together. 2.1.2.5.1 The First Dark Matter Halos, Stars, and Galaxies State-of-the-art simulations suggest that the first stars formed in gravitationally bound clumps of dark matter at redshifts between z~30 and 20. However, these mini-halos likely formed few stars, since the ionizing radiation from a single star in such a small halo may be able to dissociate and ionize molecular gas and, in some cases, unbind the halos altogether. The enriched material from these first stars seeded subsequent generations of star formation and led to the galaxies that we see at z~6-7. Empirical characterization of the first galaxies will require observations in the near-infrared (NIR). Samples of galaxies at z>6 are being produced by HST; JWST will provide samples of galaxies at even larger redshifts. Deep NIR spectroscopy is needed to robustly measure the rest-frame ultraviolet luminosity functions and infer their contribution to reionization (Figure 2-21). Near- infrared spectroscopy is also crucial to probing these galaxies for the presence of metal-free stars via high-ionization emission lines such as HeII1640. 2.1.2.5.2 Galaxies in the Early Universe Galaxies at large redshifts are generally selected on the basis of their flat (in fν) rest frame ultraviolet continuum or their strong Lyα emission lines. Ultra-deep visible and near-IR imaging HIGH LEVEL SCIENCE GOALS, KEY SCIENCE REQS, OPERATIONAL CONCEPT 2–28 GMT SYSTEM LEVEL PRELIMINARY DESIGN REVIEW December 17, 2013 surveys with HST have allowed us to characterize the overall evolution in the galaxy density from z~8 to the z~1-2 where ground-based surveys provide good statistics. Figure 2-21. The evolution of the UV luminosity density and derived global star formation rate from z~10 to the present day (from Bouwens et al., 2011)44. The rate of star formation grew rapidly in the first ~1 billion years after the Big Bang and peaked when the Universe was around 2-3 Gyrs old. Observations with the GMT and the James Webb Space Telescope will allow us to probe the first ~500 Myr for signatures of the reionization. At the time of this writing, only a few galaxies at z>7 have been spectroscopically confirmed via Lyα emission (e.g., Vanzella et al., 2011)45. Very long integrations (e.g., 15-25 hours) with 8 m telescopes have been required to yield the few detections to date. Figure 2-22. Left: VLT/SINFONI 15 h spectrum of the z=8.56 galaxy, UDFy-38135539 (from Lehnert et al., 2010)46. Right: A simulated GMT/NIRMOS spectrum of the same object with the same exposure time in black, with the 1-sigma noise spectrum in red. The significance of the detection in the simulated GMT -18 2 spectrum is ~70 sigma and the input Lyα flux is 6 x 10 erg/sec/cm . In Figure 2-22 a comparison is observed as a spectrum of UDFy-38135539 along with a simulated observation of the same galaxy with a multi-object NIR spectrograph on the GMT. Not only is the significance of the detection vastly improved, but also the sensitivity is sufficient to allow useful searches for other features. The James Webb Space Telescope (JWST) should produce large samples of galaxies at z>8. The GMT with its near-IR spectrographs will have the sensitivity to detect Lyα emission from galaxies HIGH LEVEL SCIENCE GOALS, KEY SCIENCE REQS, OPERATIONAL CONCEPT 2–29 GMT SYSTEM LEVEL PRELIMINARY DESIGN REVIEW December 17, 2013 to z~12 and perhaps beyond. At z=12 a galaxy with the same intrinsic Lyα luminosity as UDFy- -18 2 38135539 will have a Lyα flux of 3 x 10 erg/sec/cm , and thus be detectable with the GMT in a practical exposure time if the IGM is reasonably transparent at these wavelengths. The JWST spectrograph, NIRSPEC, will have great sensitivity in its lowest resolution mode (R=100) and will be highly competitive with ground-based ELTs in its R=1000 mode. The GMT, with a larger field of view and high spectral resolution will excel at studies of larger samples, line profiles, and detection of faint narrow spectral lines in clear windows of atmospheric transmission and emission. 2.1.2.5.3 Discovering the First Stars By z~15 the average metal abundance of the Universe will likely have increased above the critical value necessary for Population III star formation. Pop III stars could, however, still form in primordial gas clouds at later times and, hence, lower redshifts. HeII recombination emission is a tracer of Pop III. The HeII1640 emission line can be very bright and does not suffer from resonant scattering. Scannapieco et al. (2003)47 predicts that ~30% of L(Lyα) galaxies at z=6-10 host Pop III star formation. Table 2-3. Lyα fluxes and Lyα/HeII flux ratios for different abundances and IMFs IMF F(Lya) (1E-18) Lya/HeII Z = 0, Top-Heavy 85.0 8 Z = 0, Salpeter 8.5 40 Z = 0.0005, Salpeter 8.5 80,000 In Figure 2-23 the most recent models from Pawlik et al. (2011)48 are used to estimate the likely levels of HeII1640 emission from Pop III star-forming galaxies at high redshift. They consider three stellar populations: zero metallicity with a top-heavy initial mass function (IMF); zero -3.3 7 metallicity with a Salpeter IMF; and Z=10 with a Salpeter IMF. For a z=9 galaxy with M*=10 MSun, these three models correspond to the Lyα fluxes and Lyα/HeII flux ratios shown in Table 2-3. A Salpeter IMF with a non-zero metallicity will not produce a detectable level of HeII flux, but the two metal-free IMFs may. Figure 2-23. Left: Model of metal-free disk formation at high redshift (from Pawlik et al. 2011). Right: A simulated NIRMOS 2 h integration of a z=9 metal-free galaxy with a top-heavy IMF. HeII 1640 emission is clearly detectable. With a Salpeter IMF, this same galaxy is not detectable in HeII, thus a top-heavy IMF may be necessary to detect HeII at the highest redshifts with the GMT. HIGH LEVEL SCIENCE GOALS, KEY SCIENCE REQS, OPERATIONAL CONCEPT 2–30 GMT SYSTEM LEVEL PRELIMINARY DESIGN REVIEW December 17, 2013 2.1.2.5.4 Probing Reionization 2.1.2.5.4.1 Constraints from Lyα Emission One probe of reionization is the frequency of the occurrence of Lyα photons, a clear signature of ionizing radiation. As Lyα photons are resonantly scattered by neutral hydrogen, the frequency of Lyα emission in galaxies during reionization is sensitive to IGM neutral fractions ranging from 10 to 100% (McQuinn et al., 2007)49. Large surveys of star forming galaxies at 4 The wide-field spectrographs on the GMT will provide the collecting area and large fields-of-view needed to sample large numbers galaxies with faint Lyα emission. A 2-hour GMACS observation will reach a limiting line flux of 2-3 x 10-18 erg/sec/cm2 comparable to the measured line flux in the few confirmed z=7 sources, which required integrations over 5 times longer. In a modest investment of time (e.g., five nights) one could assemble a sample of ~200 Lyα galaxies at z>7 with the GMT. 2.1.2.5.4.2 High Resolution Spectroscopy of Quasars Lyα absorption from over-dense regions of the IGM imprints a forest of dense features on the spectra of distant quasars. As the Universe transitions from ionized to neutral with increasing look- back time, the “forest” becomes a deep opaque trough in the spectra of quasars and gamma-ray bursts (GRBs) at wavelengths below Lyα in the rest-frame of the object. Detailed studies of intergalactic absorption lines enable measurements of quantities such as the IGM temperature and metal abundances, as well as the ionization state of the IGM in the early Universe. HIGH LEVEL SCIENCE GOALS, KEY SCIENCE REQS, OPERATIONAL CONCEPT 2–31 GMT SYSTEM LEVEL PRELIMINARY DESIGN REVIEW December 17, 2013 Figure 2-24. Synthetic Lyα absorption spectra of a quasar at z=6.15, shown with the resolution and signal to noise typical of spectra obtained on 8-m class telescopes (upper), and (lower) as it would look with GMT using a high resolution (R~40,000) optical spectrograph such as G-CLEF Useful observations with 8-10 m apertures require very long integration times (>10 h). Figure 2-24 displays detailed simulations of intergalactic Lyα absorption in the spectrum of a z=6.15 quasar. The upper panel shows the normalized transmission blue-ward of the Lyα emission line against observed wavelength. The spectrum has resolution R=2800 and a S/N=20 per 3.0_Å/pixel, representative of moderate resolution and signal-to-noise data obtained with Keck/ESI for the brightest known quasars (i~22) at z~6. The lower panel shows the same spectrum, but for R=40000 and S/N=30 per 0.2 Å/pixel, representative of the improvement in resolution and signal-to-noise attainable with a high-resolution optical spectrograph on the GMT such as G-CLEF (in an 8-hour integration). The much higher spectral resolution enables the intrinsic widths of Lyα absorption lines in the quasar proximity zone (orange shading) to be fully resolved, allowing their thermal widths to be measured; the thermal state of the IGM provides a valuable indirect probe of reionization. Narrow features indicating a highly ionized IGM (which are difficult to observe in the trough of absorption in the lower resolution spectrum) are clearly apparent in the high-resolution simulation (cyan shading). The statistics of these regions may be used to place constraints on the reionization history and the ionization state of the IGM. Furthermore, the overall shape of the Lyα transmission close to the quasar rest frame is well-resolved; this may be used to identify the possible damping-wing signature of neutral gas along the quasar or GRB sight-line (Miralda-Escude, 1998)52. VISTA, Euclid, WFIRST and other large near-IR surveys are expected to produce large samples of z>7 quasars, most of which will be beyond the reach of spectrographs on 8-10 m telescopes. The GMT will be well suited to IGM studies using these quasars as probes. GRBs may provide even more powerful probes of the IGM as they can reach very bright apparent magnitudes and are known to occur at very high redshifts. HIGH LEVEL SCIENCE GOALS, KEY SCIENCE REQS, OPERATIONAL CONCEPT 2–32 GMT SYSTEM LEVEL PRELIMINARY DESIGN REVIEW December 17, 2013 2.1.2.6 Transient Phenomena Investigating transient phenomena (those with variability time-scales ranging from a few minutes to a few months) is a new frontier in astrophysical research. They represent a vast, unexplored parameter space for testing fundamental physics in powerful cosmic explosions such as γ-ray bursts and supernovae (SNe). Various synoptic all-sky surveys, such as Pan-STARRS and LSST, are designed to study the dynamic Universe by documenting new transient events, but a physical understanding of the origin and nature of these transient phenomena requires spectroscopic follow- up with large telescopes. The GMT will offer unique opportunities to exploit these survey databases to probe the early Universe and the most energetic phenomena known. 2.1.2.6.1 Optical Transients of Long-Duration Gamma-Ray Bursts GRBs are among the most energetic events in the Universe. In particular, long-duration GRBs are believed to originate in the catastrophic deaths of massive stars (see Woosley & Bloom, 2006 for a review)53. Some bursts are followed by optical afterglows (e.g., Akerlof et al., 199954; Kann et al., 200755; Bloom et al., 200956) that can briefly exceed the absolute brightness of any known quasar by orders of magnitude (Figure 2-25). Similar to high redshift quasars (QSOs), GRB afterglows can serve as a sensitive probe of “dark” intervening gas that is either local or external to the burst progenitor’s environment. Since GRB afterglows rapidly decline however, an effective exploitation of these lighthouses requires rapid follow-up spectroscopy (within 2 days) with 8-m class telescopes. Figure 2-25. Rest-frame optical light curves of luminous GRB afterglows and SN2006gy (Smith et al., 2007)57, compared to rest-frame, absolute r-band magnitudes of known QSOs from SDSS (Schneider et al., 200758; the grey horizontal band). The most luminous QSO to date is marked by the dashed horizontal line. The brightest GRB afterglow recorded was GRB 080319B. At early times, the optical transient was ~103 times more luminous than the most luminous QSO (Bloom et al., 2009). GRB afterglows are suitable cosmic probes because a large fraction (>50%) are known to originate at redshift z>2, including a growing fraction at z>6 when the Universe was less than one billion HIGH LEVEL SCIENCE GOALS, KEY SCIENCE REQS, OPERATIONAL CONCEPT 2–33 GMT SYSTEM LEVEL PRELIMINARY DESIGN REVIEW December 17, 2013 years old. The redshift distributions of known GRBs and QSOs in Figure 2-26 shows that GRB afterglows are better than QSOs for probing the re-ionization epoch at z>6. Rapid echelle or moderate-resolution spectroscopy of the afterglows is critical both for constraining the distances (and therefore the energy output) of individual burst events, and for probing the physical conditions of gaseous clouds along the lines of sight. Figure 2-26. Redshift distribution of 219 GRB afterglows identified as of November, 2010 (red solid curve), compared to the redshift distribution of i <20 QSOs found in the SDSS (black dash-dotted curve). The thin curves show their corresponding cumulative redshift distribution. GRB afterglows are as good as QSOs for probing the z=2-4 Universe and better for probing the re-ionization epoch. Figure 2-27 shows the afterglow spectrum of GRB050730 at z=3.968 obtained using MIKE on the Magellan Clay Telescope (Chen et al., 2005)59. Blue-ward of the host damped Lyα absorber (DLA) at 6040 Å is a forest of Lyα absorption lines from foreground gaseous clouds, including a classical DLA at z=3.564. These absorption features reveal the line-of-sight matter density fluctuations that are otherwise invisible in traditional galaxy surveys, and the echelle resolution (10.km/s) further allows accurate empirical constraints for the ionization state, kinematics, and metallicity of these intervening clouds (e.g., Chen et al., 2005; Prochaska et al., 200760). The absence of flux below 4530 Å indicates that few Lyman continuum photons escape the host galaxy. Red-ward of the host DLA are numerous narrow absorption features of neutral and low-ionization species in the interstellar medium of the GRB host, including excited transitions such as FeII. These excited ions were seen for the first time in a distant star-forming galaxy, and the time variation of their abundances allows us to constrain the distance of the absorbing gas from the luminous GRB afterglow. A subset of absorption features produced by different foreground gaseous clouds (color-coded by redshift) along the line of sight are also marked in the figure to demonstrate the feasibility of applying GRB afterglows as cosmic probes for studying the interstellar and intergalactic media at high redshift. Prompt localization of GRB afterglows and rapid responses of optical telescopes are critical to obtaining high-resolution spectroscopy during their brief periods of extreme brightness. Current or planned space- and ground-based facilities are capable of rapidly identifying new GRB afterglows over the next decade and beyond. For example, the current generation gamma-ray satellite, Swift, launched in November 2004, can provide nearly instant localization of new GRBs (Gehrels et al., 2004)61. In the past five years, Swift has detected over 500 new bursts, roughly 85% of which were instantly localized using its on-board X-ray telescope, or with optical-IR telescopes on the ground. The satellite is expected to continue the operation through 2015, at which time the Space Variable HIGH LEVEL SCIENCE GOALS, KEY SCIENCE REQS, OPERATIONAL CONCEPT 2–34 GMT SYSTEM LEVEL PRELIMINARY DESIGN REVIEW December 17, 2013 Objects Monitor (SVOM) (a Chinese-French space mission) is expected to be launched. Similar to Swift, SVOM is also designed to deliver rapid localization of new GRBs for ground-based follow- up. Other proposed space missions include the Joint Astrophysics Nascent Universe Satellite (JANUS; Fox et al., 201062) and the Energetic X-ray Imaging Survey Telescope (EXIST; Grindlay et al., 201063). These new satellites will deliver new, localized GRBs well into the decade beyond the Swift era. Figure 2-27. The afterglow spectrum of GRB050730 at z=3.968 obtained using MIKE on the Magellan Clay Telescope (Chen et al. 2005) Once a GRB is detected by one of these instruments, rapid follow-up observations from available ground based telescopes are vital. But the windows of opportunity for making these observations are short. The decay curves and apparent magnitudes for a large sample of GRBs strongly argue for a 15-minute response time for the most effective use of GRBs and probes of the IGM/ISM. 2.1.2.6.1.1 GRBs and the Reionization Epoch Empirical studies of the reionization epoch have focused primarily on observing the most distant 9 QSOs at z>6. However, QSOs are powered by supermassive black holes in ~10 MSun dark matter halos, which form presumably through mergers of smaller halos under the ΛCDM hierarchical formation paradigm and are substantially less common at earlier times. In contrast, the first stars 6 64 are expected to form in ~10 MSun halos (e.g., Barkana & Loeb, 2001) , which are already present at z>7. Since these stars subsequently generate GRBs, GRB afterglows can serve as a more abundant and sensitive probe of the intergalactic medium during the epoch of reionization. Observations of z>6 GRBs (e.g., Kawai et al., 200665; Tanvir et al., 200966) help to unveil the sequence in which the Universe became reionized (Mesinger et al., 2004; 2005)67 68. Figure 2-28 shows the afterglow spectrum of a GRB at z=6.295. In addition to strong and narrow metal-line absorption features that allow us to determine the redshift of the source, a damping trough is observed at 8900 Å. Interpreting the red damping wing as entirely due to the interstellar medium of 21 2 the GRB host leads to a gas surface density of N(HI)~4x10 /cm (the solid curve and inset of Figure 2-28) in the host medium. Such high density is comparable to what is seen in the denser part HIGH LEVEL SCIENCE GOALS, KEY SCIENCE REQS, OPERATIONAL CONCEPT 2–35 GMT SYSTEM LEVEL PRELIMINARY DESIGN REVIEW December 17, 2013 of star-forming regions in the Milky Way. However, a neutral intergalactic medium is also expected to contribute to the absorption trough (e.g., Miralda-Escude, 1998). Figure 2-28. A combined afterglow spectrum of GRB 050904 at z=6.295 (Kawai et al. 2006). The data were taken 3.4 d after the initial burst using the Faint Object Camera and Spectrograph (FOCAS) on the 8 m Subaru Telescope with a total exposure time of 4 hours and a spectral resolution of FWHM ~ 8.5 Å at ~9000.Å. The strong, narrow absorption features due to O0, Si+, and C+ allow an accurate redshift measurement of the host galaxy. Interpreting the damping trough at 8900 Å as entirely due to the host ISM (the red solid curve; see also the inset), Totani et al., (2006)69 estimates a host-DLA of log N(HI) ~21.6. Analyzing the red damping wing also allows us to constrain the neutral fraction of the IGM. Different curves show different model expectations. 2.1.2.6.2 Supernovae The frontier for supernova (SN) research in the GMT era will be routine, temporally well sampled optical and NIR spectropolarimetry to address key questions regarding the nature of the progenitors and explosion mechanisms. Answers to these questions bear significantly on studies of dark energy (Riess et al., 199870; Perlmutter et al., 199971). About 1 in 1000 galaxies will have a live supernova in it. Efforts should begin now to construct an efficient pipeline to deconvolve SN spectra from galaxy spectra and hence to discover and identify supernovae from spectra alone. The rate of discovery of supernovae promises to expand dramatically with the Palomar Transient Factory and Pan-STARRS. The LSST alone is expected to discover more than 100,000 supernovae per year. One in a thousand of these (or about 100 per year) may also be strongly lensed. An important task will be to decide which of this plethora of events should be studied in more detail with spectroscopy on a 20 m class telescope like the GMT. 2.1.2.6.2.1 Type Ia Supernovae Among the major outstanding issues in the study of SN Ia is proof that they arise in binary systems, and if so, in single degenerate systems, double degenerate systems, or some mix of the two. Clues to the progenitor system may arise by the detection of circumstellar matter. Search for and detection of variable Na D absorption in the early spectra of SN Ia is currently a topic of great interest (Simon et al., 2009)72. HIGH LEVEL SCIENCE GOALS, KEY SCIENCE REQS, OPERATIONAL CONCEPT 2–36 GMT SYSTEM LEVEL PRELIMINARY DESIGN REVIEW December 17, 2013 Figure 2-29. Time series of low-resolution spectra of Type Ia supernova SN 2010kg obtained with the Hobby-Eberly Telescope showing the evolution of the high-velocity CaII infra-red triplet. Note the especially broad feature in the top spectrum (1202) that may be blended with OI 7774 and the evolution of this feature to lower velocities (G. H. Marion, unpublished). Observing these features well before the peak magnitude is critical. LSST should find many SN Ia very early after explosion. Another important clue has come from the discovery and study of high-velocity Ca and Si features moving at 20,000-30,000 km/sec, as shown in Figure 2-29. The high-velocity calcium lines may arise from gas at solar abundance associated with some circumstellar medium, but the high-velocity silicon must represent freshly synthesized matter from the explosion. The observed kinematics may be associated with the collision of the ejecta with a shell of about 0.02 solar masses that lies at 15 substantially less than 10 cm in order not to contaminate the rising light curve (Gerardy et al., 2004)73. No such collisionally induced luminosity is seen (Hayden et al., 2010)74. These high- velocity features are highly polarized. Similar features are also seen in Type Ib/c supernovae. Observing these features early (i.e., well before maximum) is critical. Observing at larger redshifts with the associated time-delay may make this task somewhat less challenging and LSST should find many SN Ia very early after explosion. These features are under close study now, but the sample remains small and there will remain much to do in the GMT era. 2.1.2.6.3 Other Transient Sources In addition to long-duration GRBs and supernovae, other known transient events include short- duration GRBs and flares near galactic nuclei. Little is known about these phenomena, and significant progress is expected to occur during the GMT era with its imaging and spectroscopic follow-up capabilities. HIGH LEVEL SCIENCE GOALS, KEY SCIENCE REQS, OPERATIONAL CONCEPT 2–37 GMT SYSTEM LEVEL PRELIMINARY DESIGN REVIEW December 17, 2013 Unlike long-duration GRBs, which often display bright X-ray and optical afterglows, only a few short-duration GRBs have been detected in afterglow radiation in X-ray and optical that would allow accurate localization of these sources. While the origin of long-duration GRBs in the death of massive stars is definitively established by their association with core-collapse SNe, searches for supernova events associated with short bursts have yielded null results (Fox et al., 200575; Hjorth et al., 200576) and some of the few localized short-duration GRBs are found near old stellar populations (e.g., Bloom et al., 2006)77. To explain the short burst duration and lack of supernova association, a leading model of short GRB progenitors is binary merger, either neutron-star/neutron-star or neutron-star/black hole. This model can be tested by combining gravitational wave observations and afterglow follow-up. In a binary coalescence, the energy and angular momentum are carried away by gravitational waves. A direct association of gravitational wave detections and afterglow radiation of short GRBs therefore provides a critical test for the binary merger progenitor model (e.g., Lee & Ramirez-Ruiz, 2007)78. Spectroscopic follow-up of faint afterglows associated with short GRBs is also necessary to unambiguously establish the distances of these sources and to study the progenitor environment. Finally, a large fraction of galaxies are believed to host supermassive black holes at their centers. Mass deposits onto the central black hole due to tidal disruption of surrounding gaseous clouds and stars give rise to near-infrared flares near galactic centers. Observations of these flares provide a unique window for studying the size and spin of supermassive black holes outside of our own Milky Way. 2.1.3 Scientific Synergies with Other Major Facilities Astronomical facilities rarely work in isolation and most problems in contemporary astronomy and astrophysics are approached with a variety of observational and theoretical tools. The GMT and other ELTs will have unique capabilities, but input from other sources will maximize their impact. Similarly, a number of exciting new ground- and space-based facilities are on the horizon and these too will benefit from spectroscopic follow-up with large apertures and ELTs in particular. First light on the GMT and other ELTs is 8-10 years distant. For the present discussion, we limit our time horizon to the next decade or so. Some of the missions and facilities currently under consideration will be completed within that time frame, while others will be pushed further into the future or may be abandoned or evolve into something else. The top-level science drivers for most of the large missions or facilities under consideration are fairly similar. The US Decadal Survey79 and similar planning exercises in other communities around the world provide a broad vision of the scientific priorities for the coming decade, and a context in which to compare overlapping and complementary science priorities among the GMT and other facilities and missions. Table 2-4 summarizes the top-level science areas from the Astro2010 report, alongside those from the GMT, LSST, JWST, ALMA and SKA projects. While the SKA project is still evolving, their science goals provide a useful benchmark for the SKA path-finders (e.g., MWA, ASCAP, and PAPER) under development around the globe. While the precise terminology and emphasis in science area varies from one project to another, the overall correspondence is quite good. The GMT and other ELTs, or the “GSMT” in particular, have a strong overlap with the Astro2010 science areas. More specialized or targeted facilities have a different balance. HIGH LEVEL SCIENCE GOALS, KEY SCIENCE REQS, OPERATIONAL CONCEPT 2–38 GMT SYSTEM LEVEL PRELIMINARY DESIGN REVIEW December 17, 2013 Table 2-4. Top level Science Areas What follows is an overview of scientific synergies between the GMT and a broad range of current and future facilities operating on the ground or from space. There are strong scientific connections among all of the facilities, but there are particularly strong links to large apertures that can provide spectroscopy in the visible and near-IR. This has been true for NASA’s great observatories and sky surveys (e.g., POSS, SDSS) and will very likely be the case for the next generation of survey missions, be they on the ground or operating above the atmosphere. 2.1.3.1 Synergy with Ground-Based Facilities 2.1.3.1.1 ALMA The GMT and ALMA science missions span a broad range of topics, from cosmology and galaxy formation to studies of star formation and the energetics of the interstellar medium. A number of strong synergies exist between the capabilities of the GMT and ALMA, and there is a strong overlap with the key science priorities for both facilities. The primary areas of scientific synergy that we have identified relate to understanding the full range of gas-phase processes in galaxies and HIGH LEVEL SCIENCE GOALS, KEY SCIENCE REQS, OPERATIONAL CONCEPT 2–39 GMT SYSTEM LEVEL PRELIMINARY DESIGN REVIEW December 17, 2013 AGN, probing star formation in the Milky Way and other galaxies, and tracing the evolution of planetary systems from the proto-planetary disk phase through to debris disks and mature planetary systems. The question of synergy between ALMA and ELTs was the topic of a three-day workshop at ESO in 2009. The GMT’s location in the southern hemisphere ensures that it will sample the same region of the sky as ALMA. The two facilities will probe similar physical scales: the GMT, operating at the diffraction-limit, has a resolution of 10 mas at 1 micron, while ALMA will achieve 10 mas resolution at its highest operating frequencies. 2.1.3.1.2 LSST The scientific motivation for LSST is broad and diverse. LSST builds on the success of the Sloan Digital Sky Survey (SDSS) and adds a new dimension through the time-domain. The LSST project characterizes their mission in the broadest terms as “making a color movie of the sky”. Regular multicolor imaging of a large fraction of the sky visible from Chile will produce both a legacy of deep and accurately calibrated multi-color photometric images, and a time-series of both photometry and astrometry of objects ranging from near-Earth asteroids to the most distant quasars. The high-level science goals for LSST and the GMT overlap strongly. As a photometric survey facility, LSST will seed many scientific investigations, and a number of these will require ancillary data, particularly in the form of spectroscopy, to achieve their scientific aims. The depth of the LSST image catalogs is such that much of the new territory will be beyond the spectroscopic limits of current facilities. A cost-effective follow-up strategy will combine ELTs in Chile and Hawaii with multi-object and time-series capabilities on smaller apertures distributed around the globe. Figure 2-30. Solid angle and 5σ-depth in AB magnitude for a number of extragalactic imaging surveys. The spectroscopic limit in the I-band for ~20 h exposures for 4 m, 8–10 m telescopes, and the GMT are shown as dashed vertical lines. The GMT will be to reach the 10σ limiting imaging depth of the LSST survey fields in practical exposure times. The LSST will provide a large-area photometric database for studies of galaxy evolution. Much as the SDSS lead to a deeper understanding of the red and blue galaxy populations, LSST should provide a vital resource for galaxy evolution studies at intermediate and high redshifts. HIGH LEVEL SCIENCE GOALS, KEY SCIENCE REQS, OPERATIONAL CONCEPT 2–40 GMT SYSTEM LEVEL PRELIMINARY DESIGN REVIEW December 17, 2013 Spectroscopic redshifts and spectral diagnostics (e.g., star formation rate, ages, stellar populations, and velocities) will be critical to make use of this database, just as they have been with the Sloan survey data. LSST’s imaging survey will outstrip the spectroscopic capability of today’s 8 m apertures. This is illustrated in Figure 2-30, adapted from the LSST Science Book, comparing the solid angle and depth of various imaging surveys. Recent ambitious surveys such as the NOAO Deep-Wide and COSMOS are pushing the limits of current spectrographs. Very deep spectroscopic surveys (e.g., GDDS, GMASS) with exposure times of ~30-50 hours reach AB magnitudes of ~26 with reasonable signal-to-noise ratios. The GMT will extend this by 1.5-2 magnitudes and thus will be well matched to the depth of the LSST survey database. 2.1.3.2 Synergy with Space-Based Missions 2.1.3.2.1 James Webb Space Telescope (JWST) In the spring of 2010, ESO held a four-day conference devoted to scientific synergy between JSWT and ELTs. The science case for JWST, like that for the GMT, is built around two strong pillars: understanding the formation and early evolution of galaxies, and probing the formation and evolution of planetary systems and the stars they orbit. The strength of JWST is its great sensitivity at thermal wavelengths. While its angular resolution in the near-IR will be comparable to that of Hubble in the visible, it will fall short of that of the ELTs operating at the diffraction limit. The core JWST mission of probing first light and reionization is particularly well suited to synergistic work with larger apertures on the ground. NIRSPEC with its R=100 mode will have unprecedented sensitivity to Lyα emission at high redshifts. Large targeted or blind surveys will identify hundreds of candidate Lyα emitters at z>7. The GMT and other ELTs will have greater raw sensitivity to Lyα at R~3-5000 for redshifts that do not place the emission lines under telluric water vapor lines or on top of strong OH emission lines. In Section 2.1.2.5 we discussed the power of the GMT to explore Lyα at high redshifts. Webb can provide the key input survey datasets for the GMT, presumably in legacy fields such as the CDFS, XMM-Subaru deep field, and other multi- wavelength survey fields. In the field of exoplanet and protoplanetary and debris disk research JWST will benefit from its great sensitivity in the 2–10 micron regions. The low background offered by the cryogenic telescope above the terrestrial airglow will provide a sensitivity that cannot be matched on the ground. Webb will surely produce high-sensitivity spectra and spectral energy distributions of planets and disks. The GMT and other ELTs, however, will have better angular resolution and thus the smaller inner working angles critical for studies of massive close-in planets (e.g., roasters) and gas giants in the nearby star forming regions. 2.1.3.2.2 Euclid, WFIRST, and Other Space-Based Infra-Red Missions A number of missions aimed at probing dark energy are under consideration by NASA, ESA and other space agencies. Euclid is a candidate ESA mission that would carry out a large spectroscopic survey of galaxies for baryon acoustic oscillation (BAO) measurements of the expansion history. The 1.2 m Euclid telescope would produce a legacy database for studies of galaxy evolution, distant quasars, clustering, and large-scale structure. The Astro2010 New Worlds, New Horizons report recommended a large space-based mission aimed at dark energy and exoplanet science. WFIRST, a wide-field IR explorer, will carry out large surveys for SNe and faint galaxies for BAO studies. In the process, it will produce large multicolor catalogs of high galactic latitude sky. These will provide valuable survey databases for follow-up with ground-based ELTs and future space missions. WFIRST will operate in the 0.6-2.0 micron region of the spectrum. The legacy surveys carried out by Euclid and WFIRST should detect large HIGH LEVEL SCIENCE GOALS, KEY SCIENCE REQS, OPERATIONAL CONCEPT 2–41 GMT SYSTEM LEVEL PRELIMINARY DESIGN REVIEW December 17, 2013 numbers of z>7 quasars, as tabulated below (Table 2-5). Euclid was selected for development by ESA in October of 2011; launch is planned for 2019. Table 2-5. High redshift quasars expected from near-IR surveys 2 Survey Area (deg ) Depth (5-sigma, AB) z > 7 QSO’s z > 10 QSO’s UKIDSS-LAS 4000 Ks = 20.3 8 - VISTA-VHS 20,000 H = 20.6 40 - VISTA-VIKING 1500 H = 21.5 11 - VISTA-VIDEO 12 H = 24.0 1 - Euclid, wide (5 yr.) 15,000 H = 24.0 1406 23 WFIRST, deep (1 yr.) 2700 F3 = 25.9 904 17 WFIRST, wide (1 yr.) (4730) F3 = 25.3 - 25.5 1148 21 2.1.3.2.3 Space-Based Exoplanet Missions The Kepler mission is in the process of transforming the field of exoplanet research. Large numbers of planetary systems have been discovered and a large number of Earth-mass and super- Earth planets have been identified (e.g., Borucki et al., 2011). Ground-based follow-up of Kepler planets has been slow and this has been a limiting factor in removing contaminants (e.g., binary stars) from the transit database. Kepler has observed a single deep field in Cygnus, thus it is not well placed for follow-up observations from Chile. The Transiting Exoplanet Survey Satellite (TESS) is the natural successor to Kepler and will survey ~2.5 million bright stars distributed over the entire sky in a two year program. They anticipate finding 1000 transiting exoplanets with masses ranging from super- Jupiters to Earth-mass rocky planets. NASA selected this mission for phase-A development as part of the 2011 call for explorer missions. 2.1.4 Summary of High Level Science Goals We have presented the science case for the Giant Magellan Telescope as it occurs to our partner community as of mid-2011. Our motivation is a mix of contemporary science goals, the potential for new discoveries enabled by improved angular resolution and sensitivity, and multi-wavelength and multi-discipline scientific synergies with current and planned facilities. The science case for the GMT does not differ radically from those for other ELTs and has strong overlap with the science motivation for JWST, ALMA and other general-purpose observatories. The GMT does, however, have some unique strengths among the ELTs: Its fast focal ratio, somewhat smaller aperture, and Gregorian optical prescription lend themselves to large fields of view in seeing-limited applications. The large primary mirror segments present both challenges and opportunities. The geometry of the primary and secondary mirrors will allow for a very clean mid-IR telescope and enable some innovative approaches to the suppression of diffraction when trying to achieve very high contrast ratios at small inner working angles. Throughout this document we have tried to make quantitative estimates of how the GMT will address various current science questions and have, in many cases, simulated data to be obtained with the GMT and instruments currently under consideration. These have allowed us to sharpen our science focus and have fed-back into the instrument designs. HIGH LEVEL SCIENCE GOALS, KEY SCIENCE REQS, OPERATIONAL CONCEPT 2–42 GMT SYSTEM LEVEL PRELIMINARY DESIGN REVIEW December 17, 2013 The GMT science case flows down to a series of requirements and definition-documents that drive the design of the facility. Naturally, this is an iterative process; neither the science case nor the requirements arose entirely independently, nor is one entirely a direct flow-down from the other. There is little doubt that the science motivation for the GMT, and ELTs in general, will evolve over time. It is also likely that as the GMT project progresses technical considerations will lead to some changes in requirements. We hope that the science carried out in the first decade will be a mix of a subset of the investigations that we have outlined and new and unanticipated lines of enquiry generated by new capabilities on the ground, in space, and in the minds of active scientists. 2.2 Top-Level Science Requirements The previous sections laid out an abbreviated version of the science case for the GMT. This section describes the set of science-based requirements that flow down to design requirements for the telescope and associated subsystems, facilities, and instruments. Top-level requirements are described and the relevant requirement numbers from the requirements database are called out. These are uniquely numbered (e.g., SCI-1234) based on the order in which they are entered. The Science Requirements Document80 follows the formal structure appropriate to a requirements document. This section presents the requirements in a somewhat abstracted format and relaxes the formal language of requirements in some areas to facility readability. 2.2.1 Mapping Science Goals and GMT Requirements In Figure 2-31 we compare the main chapters of the GMT Science Book with essential qualities of the facility. These include the total collecting area, field of view, site location and other features. The relevance of each attribute to the core science areas is color-coded. All of the science areas benefit, and are often entirely dependent on, the large collecting area and small diffraction-limited image size. Others take advantage of the site, wide-field mode, ground-layer AO and other features to varying degrees. Table 2-6. Key attributes and observational techniques for each science area Sec. Topic Key Attributes and Observational Techniques 1 Introduction Discovery Space Considerations 2 Formation of Stars and Planetary Systems Mid-IR Performance, High Angular Resolution 3 Properties of Exoplanetary Systems High Angular Resolution, Precision Spectroscopy 4 Stellar Populations and Chemical Evolution High Resolution Spectroscopy 5 Galaxy Assembly and Evolution Wide-field, Multi-Object, Multiple AO Modes 6 Dark Matter, Dark Energy & Fund. Physics Wide-Field, Survey Modes, Near-IR Spectroscopy 7 First Light and Reionization Near-IR Spectroscopy 8 Transient Phenomena Rapid Response, High Sensitivity 9 Synergy with Other Facilities Balancing Optimization and Diversity Execution of the science program requires the use of a variety of observational and experimental techniques. These typically involve scientific instruments and other support hardware one level down from the top-level properties highlighted in Figure 2-31 Figure 2-32 maps each chapter and section of the GMT Science Book onto the wavelength ranges (near-UV through mid-IR) and operating modes. The latter includes seeing-limited operations and three modes of adaptive optics. The color code in Figure 2 32 is the same as in Figure 2 31 and reveals several clear, but not surprising, trends. One can see that thermal IR operations and natural guide star AO have their largest impact in studies of star and planet formation. Access to short HIGH LEVEL SCIENCE GOALS, KEY SCIENCE REQS, OPERATIONAL CONCEPT 2–43 GMT SYSTEM LEVEL PRELIMINARY DESIGN REVIEW December 17, 2013 wavelengths, at the other extreme, is most important for studies of abundances in stellar atmospheres and interstellar and intergalactic matter. Core extragalactic science benefits primarily from the central region of the operating spectral range. Red, visible, and the near-IR are the primary arenas for studies of first-light and reionization as well as much of the galaxy assembly and evolution studies planned for the GMT. The most relevant AO modes for extragalactic studies are LTAO and GLAO. This is primarily due to the low sky coverage of NGS adaptive optics. In Table 2-6 we list the primary techniques or key technical drivers for each science area. One can see that spectroscopy and diffraction-limited imaging dominate the desired of technical capabilities. Attribute Discovery Stars Exoplanet Stellar Galaxy Cosmology First Light Transient Synergy Science Area Space & Properties Pop’s Assembly & Physics & Phenom. Planets Reionization Chapter 1 2 3 4 5 6 7 8 9 Collecting area Diffraction-limited AO Wide-field Chilean site Rapid instrument change GLAO Low emissivity Very Important Important Not Relevant Figure 2-31. Mapping the science areas to key attributes of the GMT facility Figure 2-32 maps each chapter and section of the GMT Science Book onto the wavelength ranges (near-UV through mid-IR) and operating modes. The latter includes seeing-limited operations and three modes of adaptive optics. The color code in Figure 2-32 is the same as in Figure 2-31 and reveals several clear, but not surprising, trends. One can see that thermal IR operations and natural guide star AO have their largest impact in studies of star and planet formation. Access to short wavelengths, at the other extreme, is most important for studies of abundances in stellar atmospheres and interstellar and intergalactic matter. Core extragalactic science benefits primarily from the central region of the operating spectral range. Red, visible, and the near-IR are the primary arenas for studies of first-light and reionization as well as much of the galaxy assembly and evolution studies planned for the GMT. The most relevant AO modes for extragalactic studies are LTAO and GLAO. This is primarily due to the low sky coverage of NGS adaptive optics. HIGH LEVEL SCIENCE GOALS, KEY SCIENCE REQS, OPERATIONAL CONCEPT 2–44 GMT SYSTEM LEVEL PRELIMINARY DESIGN REVIEW December 17, 2013 Science Topic Wavelength AO Mode Science Book Chapter NUV VIS NIR MIR Seeing NGS LTAO GLAO Techniques Formation of Stars and Planetary Systems 2.1 From Stars to Planets AO imaging of disks 2.2 Young Stars Spectroscopy, chemical analysis 2.3 The IMF and Planets Imaging, astrometry 2.4 Disk Evolution Spectroscopy, AO imaging 2.5 System Architecture Spectroastrometry 2.6 Solar System Studies Imaging, low-dispersion spectroscopy Properties of Exoplanetary Systems Doppler, transit, & imaging demographic 3.1 Formation Models studies 3.2 Atmospheres Transit spectroscopy 3.3 Imaging Exoplanets Reflected light & thermal imaging 3.4 Habitable Worlds Precision radial velocities Stellar Populations and Chemical Evolution High-resolution spectroscopy, survey 4.1 Population Studies follow-up 4.2 Stellar Archaeology High-resolution spectroscopy 4.3 Abundances in Dwarfs High-resolution spectroscopy, photometry 4.4 Milky Way Halo High-resolution spectroscopy Integrated light spectra, AO imaging & 4.5 Globular Clusters photometry Assembly of Galaxies 5.2 Local Dwarf Galaxies High-resolution spectroscopy, photometry Near-IR spectroscopy, photometry, AO 5.3.1 Mass Assembly imaging 5.3.2 Dynamical Masses Spectroscopy, IFU 5.3.3 Gas Kinematics IFU spectroscopy Mass-Metallicity 5.3.4 Relation Rest-frame visible spectroscopy 5.3.5 Feedback & the IGM Rest-frame UV spectroscopy 5.4 Massive Black Holes IFU spectroscopy Dark Matter, Dark Energy & Fundamental Physics Cosmological 6.1 Parameters Survey follow-up, spectroscopy Multi-object spectroscopy, photometry, 6.2 LSST Follow-Up AO imaging 6.3 Clusters & Dark Matter Spectroscopy 6.4 Dark Matter in Dwarfs Radial velocity surveys First Light and Reionization 7.2 First Stars and Galaxies Near-IR spectroscopy AO imaging, visible & near-IR 7.3 Early Galaxies spectroscopy 7.4 Population III Stars Near-IR spectroscopy 7.5 Probing Reionization Red & near-IR spectroscopy 7.6 HI Topology Lyman alpha imaging Intermediate & high-resolution 7.7 IGM Spectroscopy spectroscopy Transient Phenomena 8.2 Long-Duration GRBs High-resolution spectroscopy, photometry Low-resolution spectroscopy, 8.3 Supernovae spectropolarimetry 8.4 Other Transients Rapid response spectroscopy Figure 2-32. Mapping between sections of the GMT Science Book, wavelengths and operating modes HIGH LEVEL SCIENCE GOALS, KEY SCIENCE REQS, OPERATIONAL CONCEPT 2–45 GMT SYSTEM LEVEL PRELIMINARY DESIGN REVIEW December 17, 2013 2.2.1 General and Observatory Wide Requirements A small number of general requirements set the parameters of the overall facility and its use. The GMT concept arose from an evolving series of discussions in the early 2000’s. These discussions were not driven by requirements, but rather by considerations of feasibility, performance and affordability. Thus, while we have crafted requirements that define the telescope and its basic parameters, some of these parameters predate, and thus were not derived from, rigorous science requirements. The core general requirement (SCI-0951) defines the GMT as a ground-based 25-meter class telescope capable of executing all, or nearly all, of the science cases laid out in the GMT Science Book. The motivations for defining the GMT in this manner include opening new discovery space in sensitivity and angular resolution, advancing contemporary science priorities, and exploiting synergistic capabilities with the next generation of ground and space-based facilities. Additional general requirements specify that the GMT will be designed for nighttime observations only (SCI-1006) and that the facility shall have a design lifetime of 50 years or longer (SCI-0985). The telescope will be sited at the Las Campanas Observatory (SCI-0952) following a multiyear site characterization process as documented in the site testing technical report81 and described in Section 3.12 of this document. Significant infrastructure will be required to support construction and operation of the GMT in Chile, both on the summit and at sea level. We have defined the requirements for the summit facilities (SCI-00246) and the sea level support base (SCI-00245). The summit facilities include the telescope enclosure (SCI-0953), for which we require the use of best practices to minimize wind buffeting of the telescope while ensuring sufficient flushing to maintain thermal equilibrium with the ambient air (SCI-1985) to minimize dome seeing (SCI-4395). The enclosure is also required to provide a mechanism to limit direct lunar illumination of the telescope optical surfaces (SCI-1973). The top-level general requirements are listed in Table 2-7 Table 2-7. General and observatory-wide requirements Parameter Req. No. Requirement Telescope SCI-0951 25 m class telescope Spectral Range SCI-2657 320 nm – 25 µm Use Conditions SCI-1006 Night time observing only Site SCI-0952 Las Campanas, Chile Enclosure SCI-0953 Thermal, wind performance, dome seeing Summit Infrastructure SCI-0246 Support buildings and equipment Sea Level Infrastructure SCI-0245 Logistics base and business offices Design Life SCI-0985 50 years Seismic survival SLR-0996 500 year return event Wind survival ENC-7832 65 m/sec The science requirements and associated error budgets specify stringent performance requirements and, in some areas, goals for the telescope and related optical and opto-mechanical systems. It would be unrealistic to expect these requirements to be met under all environmental conditions. Performance requirements that are specified in, or flow from, the SRD apply under the wind, seeing, seismic, weather and site conditions at Las Campanas Peak, within the conditions set by the GMT Environmental Conditions82 unless otherwise specified (SCI-1957). HIGH LEVEL SCIENCE GOALS, KEY SCIENCE REQS, OPERATIONAL CONCEPT 2–46 GMT SYSTEM LEVEL PRELIMINARY DESIGN REVIEW December 17, 2013 Table 2-8. Reference values and environmental ranges for requirements Parameter Value Notes Zenith Angle 0 degrees Image quality specified at zenith Wavelength 500 nm Fried’s parameter scaled as λ6/5, diffraction scaled by λ Field Angle 0 – 10 arcminutes Varies depending on mode Temperature -5 C to +40 C Error budgets do not apply outside this range Humidity 0 to 90% The enclosure is closed when relative humidity > 90% Wind Speed 25th - 75th Low wind speeds impede flushing, high winds may induce percentiles vibration Time of Night 18 degree twilight Error budgets apply only from twilight to twilight The Environmental Conditions document specifies the percentile range of key environmental parameters (e.g., wind, humidity) over which one can expect high performance. Error budgets are generally applicable up to the 75th or 90th percentile conditions. Exceptions include dome seeing requirements and image error budgets in the lowest 15th percentile of wind speeds. We summarize the environmental conditions in Table 2-8. 2.2.2 Telescope and Subsystem Requirements 2.2.2.1 General Requirements Some of the key aspects of the telescope and its specifications date to the conceptual design. The requirement that the telescope collecting area be 368 sq. meters after taking into account obscuration of the pupil by the secondary mirror and support structure (SCI-1014), for example, effectively restates the geometry of the primary mirror array and limits obscuration of the primary aperture. The figure of the telescope primary and secondary mirrors is specified in terms of structure functions that satisfy the requirement that, in the absence of the atmosphere, the telescope would produce diffraction-limited images at wavelengths of 500 nm and longer (SCI-10315). The requirement that the telescope produce images with FWHM of 15 mas at 1.65 µm (SCI-1015) in operation is a consequence of the primary mirror geometry and effectively states that the AO system must deliver image sizes that match the theoretical limit. Many aspects of the telescope implementation are independent of the basic architecture of the primary mirror array and have been derived from requirements based on scientific considerations. These include the spectral range over which performance is to be optimized, the image quality requirements in seeing-limited operations, and the mechanical operability of the telescope. 2.2.2.2 Spectral Range The telescope is required to operate from 320 nm to 25 microns (SCI-2657) in order to meet the diverse scientific goals laid out in the GMT Science Book. Good short-wavelength performance is required to address problems in nucleosynthesis while the long wavelength windows are required for studies of embedded star formation. This leads to requirements on optical coatings, particularly in the primary and secondary mirrors, to the effect that they should maximize throughput over the operating spectral range and minimize emissivity in the thermal infrared (SCI-1877). This requirement flows down to the system level requirements and drives our choice of a broad-band coating (Al) for the primary and secondary mirrors, at least during the early operations phase. 2.2.2.3 Seeing-Limited Image Quality The image quality requirements in the active-optics seeing-limited mode are specified relative to the best conditions delivered by the site. The best quartile seeing at LCO yields images with FWHM of 0.5” at 500 nm, the best 10% of seeing conditions produce images with 0.41”. We HIGH LEVEL SCIENCE GOALS, KEY SCIENCE REQS, OPERATIONAL CONCEPT 2–47 GMT SYSTEM LEVEL PRELIMINARY DESIGN REVIEW December 17, 2013 require that the telescope contribute no more than 10–15% (depending on configuration and field angle) image blur to the best quartile seeing. Combining the telescope image blur with the seeing in RSS results in little detectable increase in image size under all but the rarest conditions. The GMT can operate with, or without, the wide-field corrector and atmospheric dispersion compensator. For this reason we specify the image quality requirements separately for these two modes and both on-axis and at field-angles appropriate to the mode. The requirements on image size for on- and off-axis modes with and without the corrector are summarized in Table 2-9. Table 2-9. Image size requirements Requirement Image blur contributed by telescope Focal Station Field Angle Number Requirement Goal SCI-1876 Direct Gregorian On-Axis On-Axis 0.340″ 80% EE 0.280″ 80% EE SCI-3140 Direct Gregorian Off-Axis 5′ radius 0.390″ 80% EE 0.310″ 80% EE SCI-1890 Direct Gregorian Wide-Field 10′ radius 0.380″ 80% EE 0.300″ 80% EE SCI-6318 Folded Port Narrow-Field 1.5′ radius 0.340″ 80% EE 0.280″ 80% EE 2.2.2.4 Motion Control The GMT is designed to access the entire southern sky and enough of the sky north of the celestial equator to cover key equatorial survey fields, such as the SDSS equatorial strip and the Subaru deep fields. The telescope will access the sky over the full 360° range in azimuth angle and elevation angles from 30° [Goal: 25°] to 89.0° [Goal: 89.5°] (SCI-1063). Mechanical interference with the observing floor will limit the minimum elevation, but we have determined that the 30-degree requirement will allow us to meet our science goals. Table 2-10. Telescope motion requirements Mode Req. No. Notes from System Level Requirements Pointing, tracking, & guiding SCI-1071 Blind pointing to 5″ rms Non-Sidereal tracking SCI-1072 Up to 6″/min with a goal of up to 20″/min Field Derotation SCI-1875 +/- 201 degrees GIR rotation range Guiding w/o Field Derotation SCI-2682 Requires GIR Fixed-Pupil & GIR Field Tracking modes Dithering SCI-2836 Coordinated dither patterns of up to 3′ x 3′ Nodding SCI-2837 Coordinated nods of up to 3′ Scanning SCI-2834 Scan rates up to 6″/min, scan length limited by probe travel The telescope must execute a range of controlled motions to carry out science programs. These include basic pointing, sidereal tracking and guiding (SCI-1071), non-sidereal tracking (SCI-1072), and compensation for field rotation (SCI-1875). Some observing programs require precise offsets, nodding of the telescope, dithering, raster scans, and other control motion modes. Some programs, particularly those in the thermal IR or those aiming for very high contrast levels, are best carried out with field derotation disabled. This imposes requirements on the guiders and range of motion for the Gregorian Instrument Rotator (GIR). The requirements associated with these modes are summarized in Table 2-10. The precise parameters for these motions are specified in the system level requirements, and we list these were appropriate. 2.2.2.5 Adaptive Optics Requirements The GMT science program calls for three adaptive optics modes: natural guide star AO (NGSAO), laser tomography AO (LTAO), and ground-layer AO (GLAO). These modes use measurements of natural and laser guide stars fed back to a high-speed wavefront corrector to reduce the deleterious effects of atmospheric turbulence on image quality. The top-level requirements for the AO modes HIGH LEVEL SCIENCE GOALS, KEY SCIENCE REQS, OPERATIONAL CONCEPT 2–48 GMT SYSTEM LEVEL PRELIMINARY DESIGN REVIEW December 17, 2013 are listed in Table 2-11. The Natural Guide Star AO mode uses a bright on-axis guide star to provide high-Strehl correction over a small field of view. The Laser Tomography AO mode provides moderate-Strehl correction over a small field of view but with far greater sky coverage, by using laser guide stars to provide the high-order wavefront sensing. Ground Layer AO provides a far wider field of view with moderate image quality improvement by correcting only the low- altitude turbulence. The top-level requirement for diffraction-limited AO states that the GMT shall have a diffraction- limited angular resolution less than or equal to 15 milliarcseconds FWHM at a wavelength of 1.65 microns with adaptive optics (SCI-1015). Many of the scientific opportunities identified in the GMT Science Book relate to extrasolar planetary systems, massive black holes and stellar populations in extreme environments and these can be most effectively probed with angular resolutions of less than or equal to 20 mas, corresponding to 2 AU at a distance of 100 pc, or 200 pc at a redshift of 1. The NGSAO mode will enable the diffraction-limited and high-contrast (>105) science outlined in the GMT Science Book by providing high-Strehl image quality at wavelengths from 0.96 to 14 µm (goal: 0.60-25 µm) for targets with sufficiently bright, near-by reference stars (SCI-1008). The field of view is required to be limited only by atmospheric anisoplanatism and will be, under typical conditions, ~20″ in diameter in the H and K-bands. The highest contrast levels will be realized through the use of diffraction-suppression techniques, such as coronagraphy, and will reach contrast levels greater than 105 in the L′ band, with a goal of contrasts >106. Table 2-11. Top-level requirements for adaptive optics Mode Requirement Nos. Guide Signal DIQ (2.2µm) FoV Dia. Sky Coverage Notes NGSAO* 1008,1882,1883 Stars (V < 8) S > 0.75 20″ ~3% LTAO 1009,1884,1885,1886 Laser Asterism S > 0.4 30″ 50% at pole GLAO 1010,4509 Stars FWHM < 0.3″ 6.5′ 100% Median * these requirements are under revision and will be changed to S > 90% for V < 8 and S > 75% for V < 12. The LTAO mode enables diffraction-limited observations of faint targets beyond the reach of NGSAO. It will operate from the far red through the mid-IR and will enable high sky coverage. High angular resolution imaging with LTAO will yield images with S>0.3 over long integrations and covering more than 20% of the sky at the galactic pole (SCI-1884), with a goal of 50% sky coverage at the pole. One of the primary applications of LTAO is 2-dimensional spectroscopy using integral field spectrographs. The LTAO performance for this observing mode is specified in terms of ensquared energy in an area corresponding to a single spaxel on an IFU, such as the GMTIFS instrument. Our LTAO requirement for this mode is specified as delivering a K band (2.2 µm) fractional ensquared energy in 50x50 mas of no less than 40% over at least 50% of the sky at the galactic pole, over a 900 s integration, with a goal of 90% sky coverage at the galactic pole (diffraction at the telescope entrance pupil limits the ensquared energy in 50x50 mas to <0.69 in the absence of wavefront error). The use of a K=15 or brighter natural guide star in conjunction with the laser system will yield 50% ensquared energy in 85 mas x 85 mas spaxels (SCI-1886). This mode will enable 2-D spectroscopic studies of black holes, gravitational lenses, AGN, galaxies and other resolved targets with high sensitivity. The Ground Layer Adaptive Optics (GLAO) performance will be a strong function of the vertical distribution of turbulence, which cannot easily be described by a single parameter. GLAO HIGH LEVEL SCIENCE GOALS, KEY SCIENCE REQS, OPERATIONAL CONCEPT 2–49 GMT SYSTEM LEVEL PRELIMINARY DESIGN REVIEW December 17, 2013 performance is therefore defined in terms of the probability of a given level of performance being achieved over a fair sample of nights. The GLAO field of view is set to be no less than 6.5′ in diameter, with a goal of 10′ (SCI-1010). GLAO is expected to enhance the sensitivity of multi-object IR spectroscopy by providing images with FWHM less than 0.3 arcseconds (goal: 0.25 arcseconds) in the K-band under median conditions (SCI-1887). GLAO has been shown to provide some image improvement at shorter wavelengths and we require that the GMT GLAO system provide a 15% or better reduction in image size in the I-band under median conditions (SCI-4509). 2.2.2.6 Instrument Requirements Scientific instrumentation for the GMT is being developed at the Founder institutions under contract with the GMTO Project. Requirements, specifications, and interfaces for these instruments have been developed by GMTO working with an advisory committee and the instrument teams. While it is expected that most, and perhaps all, GMT instruments will be developed through this mechanism, we do require that the facility be able to support suitable instruments developed outside of the GMT project or for another facility. A small number of requirements pertain to instruments at this level. GMTO is committed to providing and supporting scientific instruments as integral parts of the observatory (“Facility Instruments”, SCI-4013) and to supporting approved instruments developed outside of the GMT project (“Principal Investigator Instruments”, SCI-1878). Support for either class of instruments is subject to guidelines established by the GMTO Board. GMT instruments are required to have a design lifetime of not less than 10 years, with a goal of 15 years, assuming routine maintenance (SCI-1100). The facility shall support the calibration of science instruments and provide the necessary infrastructure (SCI-1106) and support (SCI-1977). The telescope will support multiple instrument stations that allow for optimized scheduling, rapid response, and time-critical observations (SCI-1873). Switching between focal stations during the night will be enabled, but changes between the large instruments at the Direct Gregorian focus will generally not be supported during the night. The GMT shall provide a gravity invariant station to accommodate instruments with high stability requirements (SCI-1959). 2.3 Operational Concept In the two previous sections were described the GMT science case and the top-level science requirements. In this final section of Chapter 2, the vision for the operation of the observatory once construction is completed is reviewed, focusing on scientific operations such as operating the telescope, instruments and adaptive optics systems, and supporting scientific users through scheduling, data management, software support and on-site observing support. Technical operations will be discussed in Section 11 of this report. Before discussing scientific operations, a brief overview of the organization and infrastructure that supports scientific operations is provided. 2.3.1 Organization The overall organization of GMTO is defined in the GMT Founders’ Agreement. During the operations phase, the GMT observatory will be organized in more or less distinct, but closely interlinked, operational centers (Figure 2-33). There will be a Chile-based operations group with a sea-level facility supporting both mountain operations and overall logistics in Chile. The bulk of the operations staff will be based on the mountain and will operate in shifts or “turnos” of HIGH LEVEL SCIENCE GOALS, KEY SCIENCE REQS, OPERATIONAL CONCEPT 2–50 GMT SYSTEM LEVEL PRELIMINARY DESIGN REVIEW December 17, 2013 approximately one week. An operations center based outside of Chile, probably in the United States, will house the corporate staff and the top-level technical and scientific support staff along with a small logistics group supporting observers (e.g., proposal preparation, travel). Figure 2-33. Organizational cloud chart for GMT during the construction and operations phases 2.3.2 Facilities and Infrastructure The GMT will be located at Las Campanas Observatory (LCO) in Chile. LCO is owned and operated by Carnegie Institution of Washington, one of the GMTO Founders. Carnegie leases the GMT site at Cerro Las Campanas to GMTO. LCO has been in operation since 1963 and presently has a fully developed infrastructure of roads and utilities. The facilities described below will be upgraded, as needed, by GMTO to serve the needs of the GMT. Figure 2-34. Las Campanas Observatory and the GMT site HIGH LEVEL SCIENCE GOALS, KEY SCIENCE REQS, OPERATIONAL CONCEPT 2–51 GMT SYSTEM LEVEL PRELIMINARY DESIGN REVIEW December 17, 2013 2.3.2.1 Summit Facilities The buildings on the summit of Co. Las Campanas will include two major structures: the GMT Enclosure and the Summit Support Building. The Enclosure Building includes the following: • Enclosure base • Enclosure • Telescope pier • The telescope While the Summit Support Building includes/houses: • Observing and control room • Offices for summit staff and visitors • Instrumentation, electronics, and detector laboratories • Primary mirror washing and coating facilities • Secondary mirror integration and testing • Utilities and general equipment The summit support building will collect the operations/control functions, the basic maintenance, and utility functions in a single structure. Operation of the telescope and enclosure will be controlled from a room on the upper southwest corner of the building with clear visibility of and, at times, into the enclosure. Telescope operators, observers, and instrument and AO specialists will work in this room at night and when carrying out routine calibration and setup operations during the day. There will be a small operations console in the enclosure building to assist with commissioning, servicing, and other engineering tasks. Network and telecommunication links in the control room will be provided for remote observers to interact with the staff and instruments. Offices and workspace for observers and technical staff will be located just off the observing room. 2.3.2.2 Operations Center The Operations Center (OC) will likely be located in close proximity to one of the partner’s home institutions. For logistical reasons, the operations center will most likely be located in the U.S., but it is possible that it could be located elsewhere. The OC includes administrative, technical, and observer support for the GMT. Administrative staff includes the business/HR manager, accounting, purchasing/receiving, and administrative personnel. It will also support a technical group with a group lead, an adaptive optics group comprising engineers/scientists, and will likely employ an optical scientist and other electronic, mechanical and software engineers, and technicians. The OC will also be the base for the group responsible for the ongoing development of adaptive optics and other key capabilities. It will also provide observer support, including support for phase II development as appropriate, travel and logistical support, and scheduling. The primary GMT data archive will most likely be housed in the operations center. Numerous studies have shown that properly supported data archives provide a significant multiplier to publication rates and impacts for astronomical data. The essential function of a data archive is to capture and curate raw science data so it is not lost; additional functions support multiple uses of data and cross referencing of overlapping data from other observatories, on the ground or in orbit. The GMT data archive will include on-site storage of data at LCO for a limited period and long- term storage and curation at the operations center. GMTO will support this basic archiving of data HIGH LEVEL SCIENCE GOALS, KEY SCIENCE REQS, OPERATIONAL CONCEPT 2–52 GMT SYSTEM LEVEL PRELIMINARY DESIGN REVIEW December 17, 2013 obtained with the GMT, and may, depending on sufficient budgets, support a higher level of archival science support. The data archive will be mirrored at one or more locations to ensure easy access by all users and high up-time. The GMT Board will establish data access policies that will likely allow open access to all GMT data after a suitable proprietary period. 2.3.2.3 Science Operations Science operations include activities from proposal submission through execution of observing programs, data reduction and analysis, and publication of scientific results. GMTO will support essential aspects of science operations, including the development of tools for proposal preparation and evaluation, scheduling of observing programs, provision of documents relating to the facility, instrument, and adaptive optics, and on-site or remote support for the observers. GMTO will also provide, or facilitate the distribution of, software for data reduction and analysis and will maintain a basic data archive to secure all science data. We will track publication statistics to assess the effectiveness of the observatory overall as well as instruments and AO modes. 2.3.3 Operating Modes There are a variety of ways that the telescope can be operated to collect data, here referred to as the “operating modes”. These are not be confused with “observing modes” (e.g., LTAO, natural seeing, GLAO) that relate to different configurations of the telescope and wavefront control regimes. Figure 2-35 schematically illustrates the various modes. Operating modes that will be possible at the GMT include the following: 2.3.3.1 Investigator Directed - On-Site (“Classical”) A Principal Investigator (PI) is assigned specific hours/nights on the telescope and is expected to travel to the telescope to operate the science instrument and drive all the observational decisions during the allocated period, subject to safe operating limits of the facility. Collaborators may participate on-site or they may interact from remote sites. Support for classical observers includes telescope operators, instrument specialists who help setup and calibrate the instruments, and an on- call support staff for assistance with setting up and operating the science instrument and performing quick-look data reduction. A small operations staff dedicated to AO observing will be needed to ensure that high quality data are obtained when the AO system is in use. 2.3.3.2 Investigator Directed – Remote A PI is assigned specific hours/nights on the telescope. The observer operates the instrument remotely over a network from a remote observing station close to his/her home institution. Again, he/she drives all the observational decisions during the allocated period, subject to safe operating limits of the facility. Scripts that instruct the telescope to offset during observing programs will be executed on local machines and the telescope operator may limit the ability of remote observers to launch scripts autonomously. Remote observers may have collaborators that also participate from remote sites. Support for remote observers includes telescope operators, instrument and AO specialists to help set up and calibrate the instruments, and an on-call support astronomer for assistance with setting up and operating the instrument and performing quick-look data reduction. A higher level of on-site support will likely be needed for remote observing compared to classical observing. HIGH LEVEL SCIENCE GOALS, KEY SCIENCE REQS, OPERATIONAL CONCEPT 2–53 GMT SYSTEM LEVEL PRELIMINARY DESIGN REVIEW December 17, 2013 Figure 2-35. Operating modes supported for the GMT 2.3.3.3 Service Observing A PI is assigned specific hours/nights on the telescope. A GMTO staff member is assigned to operate the instrument and make any real-time observational decisions for the PI. The PI is largely removed from the observing process beyond any phase-II observing specifications or scripts. Experienced specialists trained on the instrument being used carry out the observations. The PI will collect the data remotely to evaluate the success of the observations. This may or may not be in real-time, depending on the type of program and whether the observations are carried out as part of a flexible queue program or on a preset schedule. Some institutions may choose to provide their own service-observing program within a block of time. A trained observer supplied by the partner may carry out multiple programs either on site or through a remote link. 2.3.3.4 Queue Scheduled Service Observing Queue scheduling is a flexible form of service observing. Staff observers will carry out observations drawn from a balanced suite of programs that use a range of right ascensions and conditions. The programs that will be carried out on any specific night are dynamically adjusted in response to the afternoon and night-time conditions. The PI typically only knows about the observations after they have begun or are completed. A limited queue may be operated to support only a subset of programs that may need rare or special conditions, or require synoptic observations. 2.3.3.5 Survey and Campaign Modes There may be instances in which the partners, or a subset of partners, wish to execute large or long- duration programs that cannot deliver the desired scientific result without a complete data set. The campaign mode is intended to support large concentrated observing programs in which a team of expert observers use the telescope and instruments to execute a major program. The teams may require special support or, more likely, will provide their own expertise and will require less support on site. HIGH LEVEL SCIENCE GOALS, KEY SCIENCE REQS, OPERATIONAL CONCEPT 2–54 GMT SYSTEM LEVEL PRELIMINARY DESIGN REVIEW December 17, 2013 The survey mode is related to the campaign mode, but is not concentrated in time. Survey programs may use a standard instrument setup over multiple observing sessions with the observations carried out in a service/queue mode or through on-site PIs. 2.3.3.6 Interrupt Mode / Target of Opportunity There are frequent opportunities to obtain time-critical observations of short-lived astronomical phenomena such as gamma-ray bursts or young supernovae. In rare instances, these observations can be transformational. The GMT will ultimately have multiple instruments ready and on-line, available for use with a mirror rotation or translation. The nearby LSST facility will provide large samples of transient targets on a nightly basis, and the GMT may wish to provide rapid follow-up for a select subset of these. Classically scheduled observing programs may need to be interrupted to support targets of opportunity. Preplanned interruptions may also take place, for example, to perform a synoptic observation. 2.3.3.7 GMTO Support for Operational Modes The science requirements and system level requirements documents call for the observatory (e.g., control system) to be designed to support all of the modes described above. Decisions to support service, queue and interrupt modes will be made by the Board on the advice of the project director and Scientific Advisory Committee prior to the start of the operations phase and will be reviewed from time to time. 2.3.4 Observing Modes The GMT will deliver images to instruments that are limited by either the properties of the atmosphere, the diffraction pattern of the GMT at the wavelength of observations, or some combination of these two limitations (Figure 2-36). This will be accomplished by supporting both natural-seeing and adaptive optics observing modes. The modes are distinguished by delivered image size, spectral range, sky coverage, set-up time, and field of view to the science instrument. As a rule, instruments will be designed for either atmospheric turbulence limited or diffraction- limited operation, but instruments that use both capabilities are not ruled out, particularly for ground-layer AO modes. Figure 2-36. Schematic mapping of observing modes by wavelength range Within the atmospheric limited mode we include seeing-limited imaging and images that are corrected for aberrations arising from ground-layer turbulence. Ground-layer corrected images are limited by upper atmosphere turbulence and have seeing-like PSFs and are far from the diffraction limit. HIGH LEVEL SCIENCE GOALS, KEY SCIENCE REQS, OPERATIONAL CONCEPT 2–55 GMT SYSTEM LEVEL PRELIMINARY DESIGN REVIEW December 17, 2013 Natural seeing observing modes rely on the imaging and tracking properties of the telescope without the use of adaptive optics. Slowly varying effects that impact image quality such as gravitational and thermal distortion of the structure and optics, tracking errors and telescope shake are corrected by the active optics system and fast-steering secondary mirrors, but rapidly varying atmospheric wavefront errors are not. Two natural-seeing modes are specified for GMT. Narrow- Field (NF) operation delivers images to the science instrument without the use of refractive correctors or atmospheric dispersion compensation. Wide-Field (WF) operations use an optical corrector to provide an increased field of view while also providing atmospheric dispersion compensation. The three adaptive optics observing modes have been described in the previous sections of this chapter. 2.3.5 Time Allocation The GMT Founders’ Agreement specifies how observing time is allocated among partners and other groups that support the construction, hosting, or operations of the facility (Figure 2-37). There are several categories of observing time, which may impact the manner in which time is allocated. Figure 2-37. Distribution of various classes of telescope time in the steady-state. Engineering time comes off the top before other allocations. Of the available time a portion is reserved for astronomers at Chilean institutions. The remaining time is distributed between “Founders Time” – time allocated in proportion to capital investments – and “Participants Time” – time awarded in return for operating funds. The Founders’ Agreement allows for a small amount of Director’s Discretionary Time, marked as DDT in the chart. 2.3.5.1 Engineering Time Observatory subsystems require preventive maintenance, re-calibration, upgrades and periodic repair. Regular engineering nights are scheduled to perform such activities and these are essential to managing unplanned downtime. Initially, the fraction of time needed for engineering will be relatively high and can be expected to ramp down as the facility matures. It is very unlikely that this fraction can be reduced below levels typically required at other observatories given the complexities of the GMT and its subsystems. The SRD provides guidance on the number of nights to allocate. The GMTO director, in consultation with the Board, will allocate sufficient engineering time to ensure that the operational and maintenance needs are met. 2.3.5.2 Contributors and Others’ Observing Time The majority of the telescope time on the GMT will be allocated to those parties that have supported the capital cost of the facility and the annual operations cost. Contributor’s time is divided into Founders’ Time and Participants’ Time. The former is allocated to the founding institutions in proportion to their Founders’ shares, derived from their time-weighted contributions to construction. Participants’ time is allocated in proportion to contributions to the annual HIGH LEVEL SCIENCE GOALS, KEY SCIENCE REQS, OPERATIONAL CONCEPT 2–56 GMT SYSTEM LEVEL PRELIMINARY DESIGN REVIEW December 17, 2013 operations budget. The relative weighting between Founders’ and Participants’ time depends on the relative contributions to capital and operations cost to the life-cycle costs of the facility. We expect that these categories of observing time will be allocated as the result of a peer-review process. At this time is it unknown if this process will be handled by each institution individually, or if there will be a central coordinating body. The GMTO Board will adopt a policy for the allocation of observing time based on input from the Director. The Founders’ Agreement states that observing time may be allocated to groups that are neither founders nor participants. This may include Chilean observers and other entities at the discretion of the GMTO Board. 2.3.5.3 Director’s Discretionary Time The GMT Founders’ Agreement specifies that the GMTO Board may allocate a fraction of observing time not to exceed 5% as Director’s Discretionary Time. The director will determine how time allocated to this pool by the Board will be used. Interested parties may submit requests to the director, or the director may identify a science topic in which he/she wishes to concentrate GMTO resources (e.g., as the STScI Director did for the Hubble Deep Field). 2.3.5.4 Time Allocation Process At this time, GMTO has not fully defined the manner in which telescope time will be allocated, as this depends on a variety of factors and the preferences of the partner institutions. Other considerations include: the types of observing modes to be supported, the interest by member scientists in pursuing campaigns, key projects, and long-term studies. The basic flow of proposals from phase 1 onwards is illustrated in Figure 2-38. Figure 2-38. Proposal processing flow from preparation of phase I proposals to through TAC review process and scheduling of observations HIGH LEVEL SCIENCE GOALS, KEY SCIENCE REQS, OPERATIONAL CONCEPT 2–57 GMT SYSTEM LEVEL PRELIMINARY DESIGN REVIEW December 17, 2013 2.3.6 User Support “User support” refers to the services and documentation provided to current and prospective users of the facility and archival data. These users may be astronomers observing on-site or remotely, or those astronomers whose programs are being executed through a queue or service mode. GMTO should provide these scientists with assistance in the following areas: • Documentation related to the facility, instrumentation, infrastructure and logistics (travel, lodging, computing) • Proposal preparation and program execution tools (phase 1 and 2 tools as needed, web forms, software) • Advice and/or assistance with preparing for an observing run • Advice and/or assistance with planning to use a facility instrument • On-site (or remote) assistance in observing with a facility instrument • Instructions for retrieving data from the science archive • Guidance for reducing data from a facility instrument 2.3.6.1 Observing Assistance For investigator directed observing, the astronomer will be either at the telescope or working remotely as if he/she is at the telescope. In general, interacting with GMT systems, including instruments, adaptive optics, and the telescope system, will be complex and the astronomer’s scientific effectiveness will benefit by having GMTO staff provide assistance with the instrument and AO operations. In general GMTO will not support novice observers, nor is the GMT an appropriate venue to learn to observe for the first time. 2.3.6.2 Instrument Handbooks Documentation will be provided for all facility instruments. The documentation will include an overview of the physical design of the instrument (e.g., light path, mechanical and optical parameters, locations of user access points such as grating and filter holders and their sizes) its performance attributes (e.g., spectral resolution, wavelength coverage, sensitivity, field of view) and guides for proposal preparation, instrument setup (including guide-star selection and aperture mask generation if applicable), data acquisition (including required calibrations and exposure estimates), and data reduction. Any special or unique observing features and modes must be described. Any limitations must be noted (e.g., cable wrap limits). If the instrument is fed an AO corrected beam, the requirements for a successful AO setup must be described (e.g., number, brightness, and distance from science target of guide/tip-tilt stars). All documentation will be available via the web, and will be maintained to reflect changes in the observing system. 2.3.6.3 Data Reduction Pipelines The effective use of complex instruments by a broad user’s community requires sophisticated data processing software. The first step in the analysis process is often referred to as a “data pipeline”. These software packages remove instrumental signatures and apply essential calibrations and generally leave the data in a state where the investigator will be able to carry out the analysis needed to complete their science program. GMTO will foster the development and curation of data pipelines and attendant calibration data with the instrument teams and observatory staff. The precise development path for the pipelines may differ depending on individual circumstances. HIGH LEVEL SCIENCE GOALS, KEY SCIENCE REQS, OPERATIONAL CONCEPT 2–58 GMT SYSTEM LEVEL PRELIMINARY DESIGN REVIEW December 17, 2013 2.3.6.4 Quick-Look Reduction and Analysis Tools Real-time assessment of data quality and signal-to-noise ratios is essential to efficient observing programs. GMTO will provide, or facilitate the provision of, quick-look data reduction and analysis tools for use by observers and staff on the summit. 2.3.7 Instrumentation and Adaptive Optics This section describes the accessibility of the GMT-instrument and AO-suite. GMTO provides technical support and maintenance for its facility instruments and AO. Support for PI instruments, should there be any, is not promised. 2.3.7.1 Multiple Instruments and AO Available GMT will aim to have more than one facility instrument available for use and in a user-ready state on any given night. Depending on the operations mode in use (classical, queue, etc.) one or more instruments will be prepared for the observing program of the night. Health checks and calibrations will be completed during the day unless other critical activities take precedence, or environmental conditions are not conducive. Table 2-12. Instrument change time matrix Initial Focal Station Final Focal Station Time Notes Instrument Platform Instrument Platform 3 minutes Rotate M3 Instrument Platform Direct Gregorian 6 minutes Retract M3 at zenith Direct Gregorian Instrument Platform 6 minutes Insert M3 at zenith Direct Gregorian Direct Gregorian 60 minutes Daytime only Gravity Invariant Instrument Platform 6 minutes Remove GIS feed, insert M3 at Zenith Gravity Invariant Direct Gregorian 6 minutes Remove GIS feed We anticipate supporting two types of instrument changes during night-time observing: changes from one IP instrument to another or from an FP instrument to an already deployed DG instrument, or the reverse. We provide the rationale for the timescales targeted for effecting the change. Changes from one FP instrument to another FP instrument are accomplished by rotating or, if an instrument requires direct access to the focus, removing the tertiary mirror from the beam: these must be fast enough to accommodate rapid targets of opportunity (see Table 2-12). In their early afterglow phase, GRBs can fade as much as 5 magnitudes in 15 minutes – a factor of 100 in flux. At later times, ~24 hours after the event, the fading in 15 minutes is a fraction of a magnitude, but the afterglows are typically 8-10 magnitudes fainter at that time. Thus the most demanding applications drive the change time to 5-10 minutes. Deployment of a fiber-fed instrument on the platform (e.g., G-CLEF) will require the retraction of M3 from the beam. Changes from an FP instrument to the fiber-fed echelle may be driven by changes in conditions or targets of opportunity (e.g., GRBs) and should be accommodated during the night on timescales of 15 minutes or less. Switching from an FP instrument to a narrow-field DG instrument is accomplished by removing M3 (or reverse). These can be accommodated during the night, provided that the DG instrument is positioned for observing. These changes must be fast enough such that the scientific benefit outweighs the lost time on the sky. Typical motivations for this change may be the rising or setting of the moon, synoptic programs, planetary transits, nearby SNe or new classes of time-critical phenomena. The time urgency here is less than in the case of rapid unpredictable transients, but the transition should be fast enough to maintain reasonable observing efficiency. HIGH LEVEL SCIENCE GOALS, KEY SCIENCE REQS, OPERATIONAL CONCEPT 2–59 GMT SYSTEM LEVEL PRELIMINARY DESIGN REVIEW December 17, 2013 It is possible that there will be a time when the GMT supports more than one tertiary mirror. Multiple mirrors may have coatings optimized for specific applications (e.g., Au vs. Al). At this time there is no concept for supporting multiple tertiaries other than changing out the mirror on the deployment arm. We do not anticipate this as a nighttime change. 2.3.7.2 Configuration All facility instruments and AO systems will be properly configured to meet the requirements of the evening’s observing program by the day staff. The nightly program will depend on the operations mode in effect for that night (classical, queue, etc.) and will be dynamically defined in the case of queue by the queue team lead. The configuration activities may include: changing/rotating gratings, changing filters, selecting the primary instruments (e.g., the DG instrument that is placed into observing position, rotating M3 to the appropriate position) and inserting/removing the Corrector-ADC. 2.3.7.3 Calibrations GMTO will provide illumination facilities to allow for common calibration of instruments. We will provide a facility flat-field calibration system for natural seeing and AO instruments with brightness sufficient to achieve 1% photon statistics with exposure times that do not compromise operational efficiency for typical pixel sizes. Instruments that require special capabilities (e.g., mid-IR sources) must include those capabilities in their design. GMTO shall provide a facility spectral calibration system for natural seeing and AO instruments that is selectable to achieve wavelength coverage over the optical and near-IR wavelength range of the GMT with a spectral line density sufficient to achieve the necessary wavelength precision. Instruments that require special capabilities (e.g., laser comb) must provide those capabilities themselves. GMTO will provide for common calibration and checks of the AO system. Daytime calibrations will be taken by members of the AO team as necessary to support the nightly observing plan. This includes any calibration necessary for the laser guide star system. 2.3.7.4 Performance Monitoring In order to guard against an instrument failure during the night, GMTO staff will assess the health of each facility instrument and AO system on a regular basis. A standard set of checks will be performed, as recommended by the instrument and AO design teams. The data will be evaluated to ensure that the instrument and AO systems are performing as expected and as required for the nightly observing plan. An abbreviated set of checks will be performed if priority activities pre- empt the health checks. 2.3.8 Performance and Success Metrics Ultimately, GMT is a research tool. The success of the facility and the effectiveness of its operating organization are measured by its contribution to the scientific knowledge base. There are several indices of merit that can be used and, while none is perfect, several are accepted in the community as valid indicators (Crabtree 2008, SPIE 7016, 40). These include: • The number of refereed papers published per year based on GMT data - this is usually called “productivity”. Publications in the technical literature (e.g., SPIE) should also be included in this metric as they reflect valuable intellectual contributions. • The citation rate and total citations of papers based on GMT data. This provides a lagging indicator of the effectiveness of the facility and its user community. HIGH LEVEL SCIENCE GOALS, KEY SCIENCE REQS, OPERATIONAL CONCEPT 2–60 GMT SYSTEM LEVEL PRELIMINARY DESIGN REVIEW December 17, 2013 • The “impact” of the papers published based on GMT data. Impact measures the citation rate of a paper relative to the average citation rate of all papers in the astronomical literature published during the same year. There are variants on this metric than can be employed to provide greater detail or precision. Many factors influence both the publication rates and impact metrics. These include the down-time of the facility, the type and effectiveness of scientific instruments, and the style of science conducted by the user community. Short projects tend to produce high publication rates, while long-term multi-facility programs tend to have higher long-term citation numbers and impact metrics. The partners, through the SAC and Board, may wish to establish incentives for one type of program over another and these may evolve over the lifetime of the observatory. Many facilities evolve from an early emphasis on short high-impact projects to longer-term key projects or surveys as the facility matures. 2.3.9 Science Data Management All science data obtained at the GMT facility, either from facility or PI instruments will be stored by GMTO. That is, all data will flow through a path that archives the information. GMTO will provide the hardware and software interfaces, and the personnel, to ensure that these data are collected and secure. Observers will have access to their data on-site or via the Internet so they can retrieve it for immediate use or to carry with them after an observing run. Remote, service, and queue observers will be notified when they can access their data through the data archive or intermediate storage. 2.3.10 Data Archive and Distribution GMTO will maintain archives for all science data for the life of the facility. A local on-site archive will be supported to ensure data security for a period of at least one month without requiring a network connection to either the sea-level facility or to the site of the primary data archive. The data archive will include science data taken as part of all scheduled observing programs along with calibration data obtained as part of, or in support of, these programs. Relevant metadata will be captured and the archive will allow one to associate proposal metadata with science data. A simple user interface will support archive queries and downloading of data via the web. Data will be made available to PIs either on site through local disk drives or through a remote access to the archive. The distribution of science data to groups other than the PI and their team will be subject to policies set by the GMTO Board. We expect that the archive will provide open access after a suitable proprietary period that protects the interests of the PIs and, in particular, students and postdocs conducting research critical to their career development. 2.3.10.1 Common Data Formats Science data from GMT instruments will be delivered in common formats. The baseline format will be the “Flexible Image Transport System” – FITS. The particular version(s) of FITS supported (e.g., multiple image extensions) will be defined as part of the instrument data system development. HIGH LEVEL SCIENCE GOALS, KEY SCIENCE REQS, OPERATIONAL CONCEPT 2–61 GMT SYSTEM LEVEL PRELIMINARY DESIGN REVIEW December 17, 2013 2.3.10.2 Data Compatibility GMT Science data and the relevant metadata will be made compliant with world-wide Virtual Observatory standards as defined at the time of the instrument preliminary design reviews. 2.3.10.3 Remote Networking Limited access to GMTO systems will be available from remote nodes. Access will be restricted to nodes that have been evaluated to be safe using protocols appropriate at the time of the start of commissioning. Remote access to, and control of, a highly restricted subset of GMT systems will likely be necessary for remote observing, and remote diagnostic and repair (instruments, data pipelines, AO components). 2.3.10.4 Engineering Data Management GMTO will collect and archive selected engineering data from the telescope, instruments, and AO systems. These data may be needed, for example, by the instrument data pipelines, or for diagnostic analysis of failures. These will be accessed through an engineering data management system. Due to the large volume of engineering data that is collected, storage of non-essential datasets will be subject to an expiration period; essential engineering data will be archived for the life of the observatory. 2.3.10.5 Workstations Astronomers will be allowed to bring their own computing equipment to the mountain. The equipment must be registered with GMTO in order to access network services, and may be subject to an assessment of its susceptibility to malware. 2.3.11 Environment The GMTO facilities will be designed and constructed to operational and survivable environmental limits as defined in Environmental Conditions document. The safe operating conditions defined in that document form the criteria for when it is safe to open the enclosure for nightly observing, and/or when the conditions warrant closing during the night. Equipment and tools must be implemented to allow decisions about the environmental safety of the observatory to be monitored, and to minimize subjectivity in decisions to open or close. During safe operating conditions, the environment is still an important aspect of operations as it will influence the quality of the data. The environmental “observing” conditions will be critical in making decisions about what the optimum observing mode is for any given time (the current conditions) or any time in the future (the forecast). To enable these decisions, equipment and tools must be provided for real-time feedback of the observing conditions, and to provide nightly statistics. In addition, tools and/or services should be provided for obtaining forecast information for the site. 2.3.11.1 Environmental Data Gathering and Statistics The environmental data that needs to be gathered to assess the operational safety of the observatory and the modes of observing will require several types of instruments and equipment. Those instruments that will be most important for ensuring safety and maximizing science are described here. The environmental data that is gathered must be accessible in real-time and be visible to the users. Environmental data may be displayed with short-term (nightly) trends, and should be stored in an archive that is accessible to users for statistical assessments. Wherever possible we expect to coordinate and collaborate with LCO in the collection and recording of environmental data. HIGH LEVEL SCIENCE GOALS, KEY SCIENCE REQS, OPERATIONAL CONCEPT 2–62 GMT SYSTEM LEVEL PRELIMINARY DESIGN REVIEW December 17, 2013 2.3.11.1.1 Weather Sensors to measure temperature and humidity inside the enclosure, along with an external weather station to measure wind speed/direction, humidity, temperature, barometric pressure, and cloud cover/opacity, are needed to assess the conditions for safe operation of the GMT. The real-time weather displays should indicate when conditions are approaching operational limits, and provide warnings if safe operating conditions are exceeded. The LCO All Sky Camera, or its next generation implementation, may provide the required cloud cover information. 2.3.11.1.2 Dust Monitoring Sensors to measure the particulate count (dust) are necessary for ensuring cleanliness of the telescope optics to ensure that throughput requirements are maintained, and to reduce the frequency of in-situ cleanings and major re-coating operations. The dust monitor is ideally located inside the enclosure in an area that experiences the free flow of air through the enclosure when open. Some form of dust monitoring outside the dome will be needed to ascertain when the enclosure can be opened after a high dust event. The operational conditions determined by the dust monitor (e.g., closing in extreme conditions) should be established after operations are underway and statistical data for the site can be analyzed. 2.3.11.1.3 Atmospheric Seeing A Differential Image Motion Monitor (DIMM) is required for monitoring the nighttime seeing conditions to allow choices to be made about the best observing program to match the seeing. The DIMM is also needed to provide the actual atmospheric seeing for comparison to the GMT delivered image quality for assessing the telescope imaging performance. 2.3.11.1.4 Atmospheric Turbulence A Multi-Aperture Scintillation Sensor (MASS) may be employed to characterize the atmospheric turbulence for verifying and optimizing AO performance to meet imaging requirements. 2.3.11.1.5 Precipitable Water Vapor A precipitable water vapor monitor may be provided to monitor water vapor and its impact on observing conditions in the near and mid-IR. 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