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Massive Spectroscopic Surveys of the Distant Universe, the Milky Way Galaxy, and Extra-Solar Planetary Systems1

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Massive Spectroscopic Surveys of the Distant Universe, the Milky Way Galaxy, and Extra-Solar Planetary Systems1 SDSS-III: Massive Spectroscopic Surveys of the Distant Universe, the Milky Way Galaxy, and Extra-Solar Planetary Systems1 January 8, 2008 1Abstracted from a proposal to the National Science Foundation, submitted in September, 2007 EXECUTIVE SUMMARY Building on the extraordinary legacy of the Sloan Digital Sky Survey (SDSS) and SDSS-II, this document presents a six-year program (SDSS-III; mid-2008 to mid-2014) that will use the wide-field 2.5m telescope at Apache Point Observatory to carry out four surveys on three scientific themes: dark energy and cosmological parameters; the structure, dynamics, and chemical evolution of the Milky Way; and the architecture of planetary systems. The Baryon Oscillation Spectroscopic Survey (BOSS) will measure redshifts of 1.5 million luminous red galaxies and Lyman-α absorption towards 160,000 high redshift quasars. By using the baryon acoustic oscillation scale as a physically calibrated ruler, BOSS will determine the absolute cosmic distance scale with precision of 1.0% at z = 0:35, 1.1% at z = 0:6, and 1.5% at z = 2:5, achieving tight constraints on the equation of state of dark energy. The high-precision clustering measurements over a wide range of redshifts and length scales will also provide rich insights into the origin of cosmic structure and the matter contents of the universe. SEGUE-2 will use the SDSS spectrographs to measure radial velocities, spectral types, and elemental abundances of 350,000 stars in numerous target categories to a magnitude limit g ≈ 19, probing the kinematics and chemical evolution of the outer Milky Way. The APO Galactic Evolution Experiment (APOGEE) will use high-resolution (R ∼ 20; 000 at λ ∼ 1:6µm), high signal-to-noise (S=N ∼ 100) infrared spectroscopy to penetrate the dust that obscures the inner Galaxy from our view, measuring radial velocities, spectral types, and detailed elemental abundances of 100,000 red giant stars to a magnitude limit H ≈ 13:5, across the full range of the Galactic bulge, bar, and disk. Together, SEGUE-2 and APOGEE will provide a picture of the Milky Way that is unprecedented in scope, richness, and detail; the combined data set will play a central role in “near-field cosmology" tests of galaxy formation physics and the small scale distribution of dark matter. The Multi-Object APO Radial Velocity Exoplanet Large-area Survey (MARVELS) will use fiber-fed interferometric spectrographs to monitor the radial velocities of 11,000 bright stars, with the precision and cadence needed to detect gas giant planets with orbital periods ranging from several hours to two years. With a unique combination of enormous numbers and well characterized sensitivity, MARVELS will provide a critical statistical data set for testing theories of the formation and dynamical evolution of planetary systems. SEGUE-2 will be the principal dark time project for the first year of SDSS-III. BOSS, which will use significantly upgraded versions of the SDSS spectrographs, will become the principal dark time project thereafter. MARVELS will be the primary bright time project through Spring 2011. Following completion of APOGEE's infrared spectrograph, APOGEE and MARVELS will share the bright time equally, sharing the focal plane and observing common fields where possible to maximize overall observing efficiency. In parallel with MARVELS and APOGEE, SEGUE-2 will obtain optical spectra of brighter stars (g < 17) in the same fields. Each of the four surveys will produce the largest and most powerful data set of its kind over the next decade, and the combination of surveys efficiently devotes all of the available observing time to a rich program of first-class science. Like its two predecessors, SDSS-III will have an extraordinarily broad impact within the as- tronomical community and beyond. SDSS-III will produce large, well calibrated, easily accessible public databases that support an enormous range of astronomical research and educational ac- tivities at many levels. An active program of education and outreach will promote the SDSS-III data and tools to K-12 and university educators and to the broader public. SDSS-III will play an important role in training the next generation of outstanding young astronomers. SDSS-III focuses on some of the most exciting areas of contemporary astronomy and astrophysics, and its discoveries will have high visibility around the world. 1 Overview The past decade has seen extraordinary progress in our understanding of the Universe, the Milky Way galaxy, and the population of extra-solar planets. A wide range of observations have converged on a consistent cosmological model that incorporates cold dark matter, a baryon-to-dark-matter ratio ∼1:6, flat space, and primordial fluctuations with the statistical properties predicted by infla- tion. This model requires one very surprising ingredient, \dark energy," which drives accelerating expansion of the Universe. Large-scale imaging and spectroscopic surveys have revealed rich, com- plex structure in the outer Milky Way, residual traces of the Galaxy's hierarchical formation history. These surveys have discovered more than a dozen new members of the Local Group of galaxies and identified thousands of the most chemically primitive stars in the Milky Way. The population of known extra-solar planets has grown from a handful to over 200. Many of the newly discovered systems are radically different from our own solar system, while others could possibly harbor life like that on Earth. The Sloan Digital Sky Survey (SDSS), both the original 5-year program and its ongoing 3- year extension (SDSS-II), has made enormous contributions across a wide span of astronomical fields, including contributions to many of the discoveries mentioned above. Along the way it has exemplified a new mode of astronomical discovery, with teams of scientists cooperating in organized, systematic surveys to produce large data sets that are made publicly available and support a rich variety of investigations. The result has been unprecedented productivity: 1500 SDSS-based papers published in refereed journals, more than five dozen PhD theses, and 16 of the top 100 cited papers in the past five years. In a recent analysis of the observatories with the highest impact on astronomy, the SDSS has been ranked at the top for three of the last four years (see x2). Building on this extraordinary legacy, we propose a six-year program (2008-2014) that will use the SDSS facilities at Apache Point Observatory (APO) to carry out four surveys on three scientific themes: dark energy and cosmological parameters; the structure, dynamics, and chemical evolution of the Milky Way; and the architecture of planetary systems. The wide field of view and efficient, multiplexed spectroscopic capability of the APO 2.5-m telescope make it ideally suited to exploit the new opportunities arising from recent discoveries in these fields. The overall program is divided into dark-time (moonless) and bright-time surveys. The main dark-time survey, which takes five years, is a precision measurement of the cosmic distance scale and the effects of dark energy (BOSS). The first year of dark time will be devoted to a spectroscopic study of the structure and chemical evolution of the Milky Way (SEGUE-2). The bright-time surveys are a high-resolution infrared spectroscopic survey that can penetrate obscuring dust to see deep into the heart of the Milky Way (APOGEE), and a highly multiplexed search for extra-solar planets (MARVELS). These surveys can observe simultaneously with each other and with an extension of SEGUE-2 that concentrates on bright stars. Each of the four surveys will produce the largest and most powerful data set of its kind over the next decade, and the combination of surveys efficiently devotes all of the available observing time to a rich program of first-class science. The acceleration of the expansion of the Universe poses the most profound question in physical science today. Even the most prosaic explanations of cosmic acceleration demand the existence of a pervasive new component of the Universe with exotic physical properties. More extreme alternatives include extra spatial dimensions or a breakdown of General Relativity on cosmological scales. To distinguish competing hypotheses, we require precise measurements of the cosmic expansion history over a wide span of time. Of the four most widely studied measurement techniques, the \baryon acoustic oscillation" method, pioneered in the SDSS, is especially attractive for its simplicity and its freedom from systematic uncertainties. Sound waves that propagate in the hot plasma of the early 3 Universe imprint a characteristic scale on the clustering of dark matter, galaxies, and intergalactic gas. By measuring this scale with tracers seen at different redshifts, we can create a \Hubble diagram" of unprecedented precision covering most of cosmic history and can thereby pin down the properties of dark energy. The Baryon Oscillation Spectroscopic Survey (BOSS) will map the three-dimensional distri- bution of 1.5 million luminous red galaxies and neutral hydrogen gas absorption in the spectra of 160,000 distant QSOs. The galaxy clustering measurements will determine the absolute distance scale with a precision of 1.0% at z = 0:35 and 1:1% at z = 0:6, extending the lever arm of the exist- ing SDSS measurements by a factor of two and improving the measurement precision by a factor of four. BOSS will provide the definitive measurement of the low redshift (z < 0:7) acoustic oscillation scale, reaching close to the cosmic variance limit, and it will pioneer a powerful new method of measuring acoustic oscillations at high redshift, with the QSO absorption analysis yielding sepa- rate, 1.5%-precision measurements of the angular diameter distance and the Hubble parameter at z = 2:5. The BOSS measurements will achieve precise stand-alone constraints on the properties of dark energy, the curvature of space, and the Hubble constant H0, and they will greatly strengthen the overall constraints on evolving dark energy when combined with complementary measurements that use supernovae, weak gravitational lensing, or galaxy clusters.
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