Sample expanded template for one theme: Physics of Galaxy Evolution Mark Dickinson

25 September 2007M. Dickinson Physics of galaxy evolution Approach: Understanding galaxy evolution requires physical diagnostics of stellar populations, chemical abundances, interstellar medium properties, and spatially resolved kinematics for very large samples of galaxies at high redshift spanning a diverse range of properties. Current 8-10m telescopes can carry out moderately large redshift surveys, but can only obtain spectra with adequate S/N for these physical diagnostics for a small number of the brightest galaxies. A 20-30m GSMT can achieve the required S/N for these measurements, and/or push observations to fainter objects, opening up much larger samples of galaxies for detailed physical investigation. A GSMT with a high-multiplex spectrograph might also accelerate the pace & size of redshift surveys by a large factor.

25 September 2007M. Dickinson Physics of galaxy evolution Measurements: – ~10 6 galaxy redshift survey (shared, at least in part, with the LSS+IGM theme), to define high-z population statistically and select objects for more detailed investigation. – High quality, moderate resolution spectra for ~10 5 galaxies for diagnosing metallicity & stellar populations – Near-IR IFU kinematic spectroscopy for dynamics, ISM physics, stellar populations, etc. Instrumental requirements: – Wide-field high-multiplex optical spectrograph – Wide-field high-multiplex near-IR spectrograph – Multiplexed AO-fed near-IR IFU spectrograph

25 September 2007M. Dickinson Physics of galaxy evolution Role of a 20-30m-class GSMT: – Optical spectroscopy: Main gain is achieving: – ~3x higher constant flux & exposure time, – or ~3x higher spectral constant S/N – or ~3x fainter flux constant S/N Enables physical diagnostics for galaxies now out of reach - particularly important where the luminosity function is steep, e.g., where now we can only study the rarest, brightest objects or lensed examples. Possible gain: ~10x acceleration of redshift surveys at constant mag & multiplex Useful, but may not beat future massively multiplexed spectrographs on 8-10m telescopes. – Near-infrared spectroscopy: More gain from AO. Work on faint, extended galaxies probably will not benefit from reaching the full diffraction limit, so sensitivity gain is probably less than full D 4. For compact galactic subcomponents, gain should fall be somewhere between D 2 and D 4. Most likely to cross critical threshold of sensitivity: 8-10m telescopes can only barely accomplish spectroscopy of the brightest high redshift galaxies. The number of accessible targets should increase very steeply by going factors of 3-10 fainter.

25 September 2007M. Dickinson Physics of galaxy evolution Telescope & site requirements: – Wide field for optical instruments – Moderate field, moderate AO correction for near-IR spectroscopy. – Does not necessarily benefit from diffraction-limited AO. Moderate AO correction over a wider field for high-multiplex instruments more valuable. Operations requirements: – Nothing unusual

25 September 2007M. Dickinson Physics of galaxy evolution Comparison with current 8-10m telescopes: – Current 8-10m facilities lack sensitivity to obtain spectra of ordinary high-z galaxies (not the rare & most luminous ones) with S/N adequate for physical diagnostics. – Current 8-10m facilities are nearly incapable of obtaining near-IR continuum/absorption line spectroscopy (even simply for measuring redshifts) of any but the very brightest high-redshift galaxies. – For extended emission, larger GSMT aperture may make it possible to collect enough light per unit solid angle from extended galaxy emission to take advantage of stronger AO correction (even if not diffraction limited), thus achieving better angular resolution for spatially-resolved studies.

25 September 2007M. Dickinson Physics of galaxy evolution Gains with aperture size: – Primarily linear scaling of limiting flux or S/N with aperture diameter for optical or NIR observations (generally not diffraction limited). – For a large spectroscopic survey at fixed instrumental multiplex to fixed flux limit, speed or sample size scales as ~D 2 – No fundamental breakthroughs scaling from 20 to 30 to 40m, but the number of interesting, accessible targets may increase steeply at fainter fluxes if the luminosity function is steep.

25 September 2007M. Dickinson Physics of galaxy evolution Precursor observations: – Ultradeep multicolor (U through z or Y) imaging survey, 25 deg 2, as for the LSS/IGM theme. LSST or other facilities can provide this. – Extremely deep, wide-field near-IR + Spitzer/IRAC imaging surveys highly desirable. – HST-resolution (or better) wide-area imaging surveys, ideally in the near-infrared, would be valuable for charactierizing galaxy morphologies in advance of target selection for IFU spectroscopy. IFU data will measure morphlogies, but having an imaging precursor survey would enable morphological target selection if desired. High resolution imaging could greatly enhance value of the deep slit (non- IFU) spectroscopic component. – Initial ~10 6 galaxy redshift survey might come from precursor facility (e.g. 8m/10m+WFMOS)

25 September 2007M. Dickinson Physics of galaxy evolution Follow-up observations: – Wide range of detailed, multiwavelength follow-up possible for interesting objects or classes of objects (imaging, other spectroscopy, X-ray, ALMA, etc.) Connection to other elements of the US System: – JWST, ALMA, future space FIR missions and/or SKA for SFR studies Archival value & data requirements: – Very high. All spectra will be useful for other studies. IFU spectra may be mined for many projects. Flux calibration very important. Accurate absolute astrometry will enable precise comparison to ALMA data.