1. FIRST LIGHT IN THE UNIVERSE Richard Ellis, Caltech 1.Role of Observations in Cosmology & Galaxy Formation 2.Galaxies & the Hubble Sequence 3.Cosmic Star Formation Histories 4.Stellar Mass Assembly 5.Witnessing the End of Cosmic Reionization 6.Into the Dark Ages: Lyman Drop Outs 7.Gravitational Lensing & Lyman Alpha Emitters 8.Cosmic Infrared Background 9.Future Observational Prospects Saas-Fee, April 2006

2. Motivation Great progress in tracking comoving star formation history but: - SF density averages over different physical situations (e.g. bursts, quiescent phases) - reliability of measures remains a big concern; no ideal method - hard to link to theory (witness how CDM is always able to match the data!) Stellar mass assembly is a more profound measurement - here we review how to do it and recent claims that CDM is in deep trouble Importance of developing mass diagnostics stressed in several early papers: Broadhurst et al, Kauffmann et al, Cohen et al, Brinchmann & Ellis

3. Galaxy masses: what are the options? Dynamics: rotation & dispersions (only for restricted populations) Gravitational lensing (limited z ranges) IR-based stellar masses (universally effective 0<z<6) K

4. Einstein Rings For a compact strong lens aligned with a background source, a ring of light is seen at a radius depending on the geometry and the lens mass, i.e. this allows us to measure the mass of the lens (SLACS project) lensing galaxy ring arising from single background source

5. Total Mass Density Profile Find total mass profile is isothermal with mass tracing light in shape and remarkably little evolution in density profile with redshift - indicates collisional coupling of gas and DM in ellipticals

6. The Fundamental Plane: Empirical correlation between size, L and  * Dressler et al. 1987; Djorgovski & Davis 1987; Bender Burstein & Faber 1992; Jorgensen et al. 1996 Considerably superior as a tracer of evolving mass/light ratio and assembly history: Dynamical mass: - no IMF dependence - Closer proxy for halo mass Tough to measure: -  demands high s/n spectra - large samples difficult

7. Evolution of the Fundamental Plane (Treu et al 2005) 142 spheroidals: HST-derived scale lengths, Keck dispersions Increased scatter/deviant trends for lower mass systems? If log R E = a log s + b SB E +  Effective mass M E   2 R E / G So for fixed slope, change in FP intercept  i   log (M/L) i

8. Evolution of the Intercept  of the FP Strong trend: lower mass systems more scatter/recent assembly

9. Stellar Masses from Multicolor Photometry Spectral energy distribution  (M/L) K Redshift  L K hence stellar mass M log mass spectral energy distribution Mass likelihood function

10. What if you don’t know the redshift? Catastrophic errors securing photo-z & masses from same photometry Bundy et al astro-ph/0512465 z spec  logM Expected scatter based on photo-z error distribution

11. What if you only have optical photometry? Bundy 2006 Ph.D. thesis z spec A key ingredient in the mass determination is infrared photometry which is sensitive to the older, lower mass stars; important z > 0.7 log M opt - M IR BRI vs BRIK log  (M opt )log  (M IR )

12. Stellar Masses at z~2 with and without IRAC Shapley et al 2005 Ap J 626, 698 Requirement for K-band at z~1 suggests IRAC useful at z > 2 M(no IRAC) vs M(IRAC) Masses of LBGs @ z~2

13. Shapley et al 2005 Ap J 626, 698 Effect of Recent SF Bursts on Derived Mass M(4.5  m) log mass Weak correlation of mass with long luminosity dependent on bursts R-K Correlation of mass with color confirms recent activity important to take into account  15

14. Results: Stellar Mass by Morphology Early result: the decline in stellar mass in late-types occurs at the expense of a modest growth in that of regular spirals & ellipticals, i.e. tranformation (Brinchmann & Ellis 2000 Ap J 536, L77) Comoving mass density M  Mpc -3 Redshift

15. Downsizing: SFR & Stellar Mass Density Low mass galaxies are more active in terms of SFR/stellar mass at recent times (Juneau et al Ap J 619, L135) SFR/volume by massMass/SFR

16. Stellar Mass Assembly by Type in GOODS N/S Bundy et al (2005) Ap J 634,977 No significant evolution in massive galaxies since z~1 Modest decline with z in abundance of massive spheroidals, most change at lower mass Bulk of associated evolution is in massive Irrs 2dF ( h = 1 )

17. Caveat: Dry Mergers? Caveat: Fundamental Plane measures the ages of the stars in galaxies of different masses. Young ages are seen for stars in low mass galaxies and old ages for stars in massive galaxies..seemingly in contrast to hierarchical predictions. van Dokkum (2005) argues high preponderance of red tidal features & red mergers in local samples, coupled with a postulated increase in merger rate (1+z) m implies significant mass evolution is still possible in large galaxies: i.e. stars could be old but assembled mass could be younger via self-similar merging of red sub-units (so-called `dry mergers’)

18. Dry Mergers at High Redshift Clusters: Tran et al (astro-ph/0505355) Field: Bell et al (astro- ph/0506425) No good statistics yet on how prevalent this process is

19. Palomar-K + DEEP2 Sample Palomar WIRC 2048 2 HgCdTe imager: 8.7 arcmin FOV DEEP2: R < 24.1; 4 fields (incl. EGS, can test cosmic variance) 12,121 DEIMOS redshifts z<1.5 with K<20.0 (1.5 deg 2 ) Goal: explore role of star formation & environment on mass assembly Star formation indicators: (U-B) 0 from CFHT photometry [OII] equivalent width, DEIMOS spectra (z > 0.7) Environmental density: Use nth spectroscopic neighbor diagnostic with DEEP2 redshifts (Cooper et al 2005) Bundy et al (astro-ph/0512465)

20. Color Bimodality in the DEEP2 Redshift Survey 0.75<z<1.0 1.0<z<1.40 Rest U-B

21. Downsizing & Star Formation Using rest-frame U-B color as a discriminant, a threshold stellar mass is apparent above which there is no SF Cross-over mass (red=blue) also increases with z Mass threshold increases from 10 11 M  at z~0.3 to 10 12 M  at z >1 Stable from field-to-field (V/bin~2.10 6 Mpc 3 ) Bundy et al (astro-ph/0512465)

22. The `Declining Blues’ become the `Rising Reds’

23. Theoretical Concepts of Feedback Mergers fuel AGN which expel gas and prevent further star formation (Springel et al 2004). Simulated Disk Merger with AGN Feedback age AGN feedback arising from hot gaseous halo leads to early suppression of cooling SF in massive stellar systems reproducing `downsizing’ (Croton et al 2005)

24. Massive Galaxies @ z=2: Is CDM in Crisis? Dickinson et al 2003 HDF-N photo-z Glazebrook, McCarthy et al 2004 GDDS spectra Kong et al 2006 pBzK counts van Dokkum et al 2006 census of z>2 masses

25. Comparison of Old Semi-Analytic Predictions Expect strong decline in abundance of massive spheroidals with redshift, But, in detail, the theoretical predictions are very sensitive to assumed assembly particularly for high masses where mass function is steep Benson, Ellis & Menanteau MNRAS, 336, 564 (2002) zz  N(>10 11 M o ) Mpc -3 Durham Munich

26. Dickinson et al (2003) HDF-N Pioneering study: N=737, H<26.5, z photo <3, 5 arcmin 2 H=26.5 incomplete Significant uncertainty estimating contribution of H-faint low mass galaxies z>1.5 50% of the assembled mass is only in place at a surprisingly low redshift z~1 Integrated SFH underestimates mass assembly: dust, cosmic variance? Similar HDF-S analysis by Rudnick et al 2003 Ap J 599, 847 2dF

27. Gemini Deep Deep Survey: Stellar Masses Glazebrook et al Nature 430, 181 (2004) Color pre-selected spectroscopic sample K<20.6, I<24.5 N=240 in 4  30 arcmin 2 fields 0.5<z<2 BG IMF (~0.55 Salpeter in M/L K ) Surprising abundance of massive galaxies at z>1.5 Many are `red and dead’

28. Glazebrook et al Nature 430, 181 (2004) Gemini Deep Deep Survey: Slow Mass Assembly Growth rate slower than semi-analytic models (without AGN feedback) Rate ~independent of mass so problem for M > M  10.5 particularly acute

29. Census of Stellar Mass 2<z<3 van Dokkum et al astro-ph/0601113 FIRES+GOODS+MUSYC: N~300g, 2 10 11 M  galaxies are DRGs(77%) - LBGs constitute only 17% No single technique complete in estimating assembly history DRG LBG

30. Summary of Lecture #4 Techniques are now well-established for estimating the stellar masses of galaxies to high redshift; reliability depends on having spectroscopic redshifts and long wavelength data It is now clear that mass assembly since z~2 does not proceed hierarchically; growth is suppressed in high mass systems at early times continuing in low mass systems to z~0 (`downsizing’) AGN feedback may be able to reproduce this behavior in  CDM models, but further work is needed to understand environmental dependence of this process: are downsizing trends occurring at a different rate in clusters vs `field’? Massive galaxies are now being found at z>2 in surprising numbers; many are already passively evolving. This implies much SF activity at higher redshift