1. The Formation and Evolution of Galaxies What were the first sources of light in the Universe? How were luminous parts of galaxies assembled? How did the Hubble sequence of galaxy morphologies form? How do galaxies interact with their environment? What are the global histories of star- formation, metal enrichment, and gas consumption? What is the relationship between active galactic nuclei and their host galaxies? z = 1000 z = 0 When? … and what are the baryons doing?

2. Key NGST capabilities for high z galaxies Follow hot (“young”) stellar light ( > 1200 Å) to very high redshifts z ~ 30 Trace cool (“old”) stellar populations ( > 4000 Å) to z ~ 10 Observe diagnostic emission (and absorption) features 3700 – 6600 Å at 1.5 < z < 6.5 … all this at kpc-scale resolution at all z Thermal dust emission and mid-IR diagnostic features (e.g. 3.3  m and 7.7  m PAH) of far-IR energy sources Stellar features (H-, CO) at 2 < z < 3 that are immune to dust obscuration and present in stars of age 10 7 <  < 10 10 yr Ly  at z ~ 4 and 2000 Å at z ~ 2 3 x resolution and 9 x sensitivity of HST 5 – 10  m 10 – 30  m 0.5 – 1  m Dressler core 1 – 5  m

3. Extending the frontier: Ultra-Deep Imaging 0.5–10  m Extreme depths: AB ~ 34 in 10 6 s Extreme redshifts: Lyman  to z = 40 (?) 4000 Å to z = 10 4 x 4 arcmin 2 NGST should detect 1 M O yr -1 for 10 6 yrs to z  20 and 10 8 M O at 1 Gyr to z  10 (assuming most pessimistic  = 0.2) 5000 galaxies to AB ~ 28, x 10 to AB ~ 34? photometry, morphology and redshift estimates

4. The physics of galaxy evolution: Diagnostic 1-5  m Spectroscopy Key emission-line diagnostic features in 3727 – 7000 Å range are within 1 – 5  m for 1.7 < z < 6.6, (c.f. ultraviolet “desert” at shorter  ) Star-formation rate from H  Metallicity from R 23 = [OII]+[OIII]/H  Reddening from H  /H  AGN/stellar from [OIII]. [NII], [SII], [OI], S[III] Ages from continuum features A: Physical conditions (R ~ 1000) B: Kinematics  masses (R ~ 3000–10000) Spatially resolved  rotation curves in gaseous line emission, e.g. H  within 1–5  m for 0.5 < z < 6.6 Spatially unresolved velocity dispersions in stellar absorption lines, e.g. Mg 5175, Ca triplet, and CO bands at 2.3  m (at AB ~ 24) Diagnostics not only give physical conditions but also enable associations to be made between members of the population at different epochs.

5. Inside the galaxies: Spatially Resolved Photometry and Spectroscopy Photometric and spectroscopic analysis of components within galaxies shows nature of star-formation, possible importance of merging, and the emergence of present-day morphological components HDF analyses limited to small number of bright objects at lesser resolution

6. Unveiling the hidden Universe: The mid-infrared We know from COBE that 50% of the luminous energy in Universe emerges in far-IR – apparently an important contribution from ULIRGs at high z NGST may be required to identify sources at 1–5  m, and at 30  m is potentially the most sensitive detector of thermal dust at z ~ 2 Spectroscopy of the 3.3  m and 7  m PAH features can characterize the energy source as starburst or AGN … for the complete observational picture

7. New windows on galaxy evolution: Supernovae as probes of chemical evolution and star-formation NGST can detect supernovae to very high redshifts Expect 5–15 SN II yr -1 per 4’  4’ field at z > 2, and 1–10 yr -1 at z > 4, I.e. of order 1 on every deep image. SN II give measure of star-formation rate. The effects of the time lag between SN II and SN Ia in the early Universe is seen today in  -enrichment and r- and s-process metallicity effects in Galactic halo HST z = 0.5

8. The DRM programs in “The Formation and Evolution of Galaxies” 1. Deep Imaging Survey: 0.6–10  m imaging of 1 x UltraDeep Field 16 x Deep Fields 2. Deep Spectroscopy Survey: 1–5  m spectroscopy of 100 galaxies R=100 for deep identifications; 2500 galaxies R=1000 diagnostic spectroscopy 200? galaxies R=5000 kinematics (incl.10  m) spatially-resolved 2-d integral field spectroscopy 3. Clusters: Imaging and spectroscopy of high z clusters for direct comparison with field galaxies 4. AGN–galaxy connection: Imaging and spectroscopy on high z AGN hosts (esp. Type I) 5. Obscured objects: Extension of deep imaging to 30  m with low R spectroscopic follow-up for diagnostic features 6. Supernovae: Spectroscopic follow-up of SN discovered in imaging surveys

9. Summary: NGST capabilities NGST will extend the redshift domain and should detect the “first light” † in the Universe NGST will provide a wealth of diagnostic information on high redshift galaxies, 1 < z < 5, when most stars in the Universe likely formed, that would be extremely hard to obtain in any other way. NGST’s wavelength extension down to 0.6  m gives maximum spatial resolution and the use of Lyman features at 4 < z < 9 and 2000 Å at z ~ 2. Extension longwards to 10  m gives NIR stellar features to z ~ 3–5 and extension to 30  m gives detection of thermal dust emission and diagnostic 3.3/7.7  m PAH features. NGST capable of yielding large numbers of systematically studied galaxies over very wide redshift range allowing full interpretation of individual objects within the population. † first light = star-clusters or significant AGN accretion (e.g. 10 8 L O at 1200 Å at z ~ 20  =0.2)

10. The Dressler Report “HST & Beyond” “7.2 Fundamental questions in high redshift astrophysics” 1. What was sequence of mass accumulation in central regions of galaxies 2. What was the sequence of disk formation? 3. When and where were the first heavy elements formed? 4. What was the role of AGN in galaxy formation? 5. How do the above depend on environment mass, state of the primordial gas and dynamics? 6. What were the conditions in the dark ages 1000 < z < 5? 7. Were there precursor events that preceded full-blown galaxy formation? “7.3 Generic capabilities required” 1. Wide wavelength coverage (ideally 0.5  m to 1 mm) 2. Deep imaging at high spatial resolution 3. Spectroscopy at R > 10 3, with spatial resolution 4. Large samples to be studied in survey mode Detection – identification – characterization – placement in context NGST

11. Will the NGST high-z science be done before 2008? (1) Progress since 1995 1. The 3 5 2. The HDF and morphologies and sizes at high redshift 4. Measures of metallicity in the Lyman  forest and DLA systems 5. Detection of far-IR background and preliminary identification of ultra-luminous sub-mm sources at high redshift 3. The ultraviolet luminosity density L (z) relation 0 < z < 5 0. Large redshift surveys at 0 < z < 1  (a) earliest activity must be at z >> 5 and likely distributed amongst small units (b) importance of “small and faint” galaxies at high z (c) need for physical understanding rather than just “phenomenology” (d) our present view is very biased towards (1) active star-formation and (2) the unobscured objects These continue to strengthen the case for NGST !

12. Will the NGST high-z science be done before 2008? (2) Progress to 2008 1999–2008 will see: (a) a vast increase in number of 8m nights (x 17) (b) introduction of near-IR spectrographs in 1–2  m waveband, including MOS (c) continued implementation of AO in the near-IR (d) Impact of NICMOS data and ACS (+WF3) on HST (e) SIRTF By 2008, it is reasonable to expect: (a) 0 < z < 1 will be thoroughly “done” with samples of 10 5 galaxies (but this is not where galaxies are assembled!) – this provides ideal complement to NGST programs at higher redshifts (b) Ground-based IR imaging/spectroscopy + SIRTF will yield produce large samples with redshifts 1 < z < 4 (for luminous galaxies) and we will know when large mature galaxies first appeared. Will probably not know “how” since diagnostics and masses will be difficult with spectroscopy from ground. Bias towards star-formation will remain at highest redshifts. (c) Highest redshift will creep up despite redder wavelengths and fainter fluxes. Unlikely we will reach the limit, and even if we do, it is very unlikely that we would know that we have!

13. The outlook for NGST It is reasonable to be pessimistic about ground- based observations for: (a) all deep observations at > 2.2  m (b) systematic multi-line spectroscopy at 1 < < 2  m (OH emission and H 2 0 absorption) (c) anything requiring diffraction limited imaging at  < 1  m or (wide-field) imaging at 1 < < 2  m (c.f. AO) i.e. modest progress in programs involving: (d) the very highest redshifts (e) systematic diagnostic spectroscopy (f) stellar (CO-bandhead) masses at high z (g) the energy sources in all except the most luminous high z ULIRGs (c.f. SIRTF) These are the central goals of NGST program on the formation and evolution of galaxies, which are therefore likely to remain current IR astronomy from the ground