GMT Science Use Case

GSMT Science Use Case

Title: 30m-class Follow-up Observations of JWST Imaged Galaxies & AGN

Authors: Chris Packham (Florida), Almudena Alonso-Herrero (CSIC, Spain), Nancy A. Levenson (Kentucky, USA), Rachel E. Mason (Gemini) & Pat Roche (Oxford, UK)

Summary Table:

Summarize the observations in terms of telescope, instruments, number of nights, observing mode and instrument and AO requirements.

Telescope Instrument # Mode λ λ/δλ AO FOV Nights range(μm) Mode GMT MISE A few Imaging & N (imaging R~10 MIR 15”+ tens of lo-res & spec.) & 0 AO nights spectroscopy Q Band (imaging) TMT MIRES A few Imaging & N (imaging R~10 MIR 15”+ tens of lo-res & spec.) & 0 AO nights spectroscopy Q Band (imaging)

Scientific Motivation:

Why is this use case of scientific interest?

The fueling of black holes occurring in active galactic nuclei (AGN) is fundamental to the evolution of galaxies. AGN themselves are largely explained in the context of a unified theory, by which a geometrically and optically thick torus of gas and dust obscures the AGN central engine. The exact properties of the torus remain uncertain, and there are still several open questions: (a) What is the nature of the torus material and its connection with the ISM of the host galaxy, (b) How do the properties, such as, geometry and optical depth, of the torus depend on the AGN luminosity and/or activity class, (c) Do the dust properties change with the AGN luminosity/type, and (d) What is the role of nuclear (<100 pc) starbursts in feeding and/or obscuring AGNs? Observations at mid-IR (MIR, 7-26µm) wavelengths are essential to these investigations as the torus intercepts and re-radiates a substantial amount of flux from the central engine, peaking in the MIR.

We propose to obtain high spatial resolution images and low-spectral resolution spectroscopy of AGN and luminous IR galaxies (LIRGs). These observations will be made in synergy with the results that will be obtained from the JWST and hence are analogous to the recent observations we have made using Gemini to help to fully interpret the Spitzer observations. In both the Spitzer and JWST epochs, only the superior spatial afforded by the largest ground based telescopes observing at the diffraction limit, allows the AGN, star formation sites, and diffuse emission to be disentangled from each other. Such observations are crucial to understand the local universe for application to more distant objects. JWST observations will form the foundation stone of understanding galaxy and AGN formation, where black hole and AGN evolution may become evident. However, it is clear that even JWST observations will have contamination from emission from diffuse HII regions, necessitating the use of 30m class telescopes. We note that a z=0.5, the spatial resolution of JWST is 1.5kpc (including galactic star forming rings, etc.), whereas for the GSMT the spatial resolution is 330 pc (nuclear dominated). JWST will be an outstanding resource for taking integrated imaging and spectroscopic observations of AGN and galaxies, but only the spatial resolution afforded by the GSMTs will allow targeted and fine scale investigations of the JWST results.

As an illustration of the type of synergistic work one can perform from 30m ground based telescopes and that of the JWST, we show a comparison of images and spectra taken from the Spitzer and Gemini at similar wavelengths below (see for example Alonso-Herrero et al. 2006, Diaz-Santos et al. 2008).

To illustrate the differences this can cause to the observed spectrum of galaxies, we show below a comparison of Spitzer (~600 pc) and T-ReCS (~60 pc) spectra of NGC3256 (Diaz-Santos et al., in prep), showing significantly different results. In this case, silicate absorption is essentially only from southern condensate whereas PAH dominates the nucleus, as shown when comparing the T-ReCS spectra (dotted) to the Spitzer spectra (solid). Note in the figure below the very substantial variation between the T-ReCS and Spitzer spectra due to the different extraction aperture sizes, where surrounding diffuse emission can easily confuse and contaminate the spectra, possibly misdiagnosing any present nuclear activity, star forming regions, and the torus parameter.

Approach:

How can you use TMT and/or GMT and their candidate instruments to address this problem? Describe the observing strategy, including target selection and the needed measurements. We plan imaging observations using MISE and MIRES through either broad band N or through the 1µm wide filters with λc~8.7μm. We will use these observations to plot color-color diagrams to investigate the star formation rate, with minimal contamination from surrounding emission sites. We will obtain a Q band image, which when combined with other data, helps to strongly constrains models of local dusty environments. We also plan N band spectroscopic observations of the central regions, which will allow an unprecedentedly precise view of the torus, allowing key predictions of the so-called clumpy model of AGN to be probed (Nenkova et al. 2008a, b). Clumpy models suggest that the torus is compact, necessitating the use of the highest available spatial resolution MIR observations. If available, polarimetry of the nuclear regions will be used.

Targets will be selected to form a homogenous survey of AGN and LIRGs across a wide range of luminosities. There are already observational and theoretical hints that the AGN, torus, and host galaxy are affected by the level of accretion, and a high spatial resolution MIR survey presents an ideal method to probe the activity and its effects on the host galaxy. Where possible, targets will be selected to follow-up ongoing MIR surveys from existing 8m class telescopes and observations from the JWST. The number of sources to produce a sample could number in the 100-200 objects.

Limiting Factors and the Current State of the Art: What are the limiting factors for this problem (e.g. sensitivity, spatial resolution, time resolution)? Why hasn’t this problem been solved with current facilities? Previous observations have been limited to by the sensitivity and spatial resolution of the 8m telescopes. We note that if the D4 gain in observational speed (and with all other parameters remaining equal, such as thermal background) is realized on the GSMTs, this would result in a speed increase of ~200 times that of the existing 8m telescopes. Despite this, the JWST will maintain a 1-2 order of magnitude better point source sensitivity over that of the GSMT’s, but with a factor of ~4 times worse spatial resolution. We therefore encourage the development and optimization of high spatial resolution imaging and spectroscopy on the MIR instrumentation of the GSMT’s. Further, we encourage the use of novel observing modes, such as the already envisioned nulling mode of MISE, and the adoption of polarimetry (as discussed below). It is our understanding that the brightness limits of the JWST will preclude observations of objects brighter than 4mJy, leaving many of the brightest and often ‘favorite’ objects for the GSMT in this epoch. Finally, we note that maintaining high image quality or high Strehl ratios on the existing 8m class telescopes in the MIR has been challenging. As the high spatial resolution domain is a key area of MIR GSMT science, we encourage the careful consideration of this during the design phases.

Comparison of point source sensitivity of contemporary IR and submillimeter instruments to MIDIR on a 30/42/60 m ELT. Taken from the MIDIR E-ELT conceptual design study.

Technical Details:

How would you actually carry out this program? Justify the sensitivities, exposure times, number of fields, total cost in terms of telescope hours or nights. Mode of observation, queue, classical, TOO, synoptic etc. The observations would ideally be made in queue mode. The number of objects, to make a detailed survey, could number around 100-200. Whilst just a very approximate estimate, each observation may take 2-5 hours. Preparatory, Supporting, and Followup Observations:

What data are needed in advance of, or in support of these projects? If these require observing time on 4-10m class telescopes estimate the amount of time needed. What followup observations are needed? These observations would in many senses be complimentary to JWST observations, and existing programs of observations on the current 8m class telescopes will form essential preparatory work.

Anticipated Results:

What would you expect to get from the observations? Describe simulated data and results where appropriate. Please see the above scientific motivation.

Requirements and Goals Beyond the GMT and TMT Baseline Instrument Designs:

Are there capabilities needed for this science that are not in the TMT and GMT telescope, AO system and baseline instrument configurations? If so, what is the flow-down from the high level goals to the instrument requirements? High spatial resolution imaging and low-spectral resolution (R~100) spectroscopy is needed for this program. We note that MISE have these capabilities, but that MIRES does not, and we encourage the adoption of these modes in MIRES.

Polarimetry is highly desirable, and would help to clearly distinguish the GSMTs from the JWST’s capabilities, as there is no polarimetry on the JWST, nor other upcoming space-based missions at IR wavelengths (to our knowledge). We note in general that polarimetry would be a highly desirable mode on the GSMTs. The polarimetric community is small but significant, and we note that ~9% of time requests on instruments that offer polarimetry (using the WHT’s ISIS as a guide) as a standard mode are for imaging- and/or spectro-polarimetric observations. Polarimetry has proven fundamental to addressing comets, debris discs, & AGN, but is a particularly ‘photon-hungry’ and high spatial resolution application. As there is little or no deployment on space based observatories it is a clear area of exploitation-space open for GSMT at all wavelengths.

Describe the need for specific observing conditions or operations mode(s) (needed image quality; atmospheric transmission; need for ‘interrupt-driven’ observations) Queue mode observations for MIR observations have proven crucial to matching the often specific observing constraints optimal for observations of this type. Diffraction limited observing will also be fundamental to realizing the potential of this science case.

Describe the potential of the resulting database for ‘mining’ in service of carrying out complementary scientific programs; planning future programs Describe the potential role of other ground- and space- based facilities in carrying out the proposed investigation (e.g. JWST; ALMA; LST) As noted above, these observations are complimentary and synergistic with JWST.

Summary: