Interpreting stellar populations in a cosmological context

1. Interpreting stellar populations in a cosmological context rachel somerville MPIA with thanks to the GOODS & GEMS teams, S. Faber, B. Allgood, J. Primack, A. Dekel, & R. Wechsler

2. Stellar populations can be used to ‘weigh’ galaxies Bell et al. 2003 Papovich et al. 2002

3. massive galaxies (both old/evolved and dusty/star forming) are being discovered in significant numbers at redshifts as high as z=2… stellar mass Fontana et al. 2004 (K20) Glazebrook et al. 2004 (GDDS); Brinchmann & Ellis 2000; Cohen et al. 2000; Rudnick et al. 2004 (FIRES); Drory et al. 2004 (MUNICS); van Dokkum, et al. 2004 Dickinson et al. 2003 (HDFN)

4. Do massive galaxies at high redshift pose a crisis for CDM? local galaxies m*>2.5E10 Msun m*>1.0E11 Msun LBGs K20 EROs sub-mm these kinds of observations could refute CDM, but so far they do not pose a problem. n.b. all theorists agree on this SDSS QSOs

5. the overcooling problem halo mass function cooling+SF …+squelching …+SN FB …+ merging suppressed in clusters need to suppress cooling and/or star formation in massive halos to fit z=0 stellar mass function and luminosity functions

6. Stellar mass assembly history: comparison with LCDM models Glazebrook et al. 2004 Fontana et al. 2004

7. stellar mass assembly history good agreement with observational estimates Glazebrook et al. (GDDS) Rudnick et al. (FIRES) Dickinson et al. (HDFN) Fontana et al. (K20) Borch et al. (COMBO-17) Somerville et al. (GOODS) Tecza et al. 2003 (SMG’s) IMF=Kroupa

8. why do galaxies come in two basic types? spheroidal, dynamically hot red colors strong absorption lines predominantly old stars little recent star formation thin disk dynamically cold supported by rotation blue colors strong emission lines broad range of stellar ages, ongoing star formation

9. galaxy colors (and many other properties) are strongly bimodal red color blue bright faint luminosity SDSS Baldry et al. 2003

10. red color blue bright faint luminosity SDSS Baldry et al. 2003

11. The two types are divided by a critical mass old, no recent star formation, high concentration/surface brightness ~3x1010 Msun old young young, recent star formation, low concentration/surface brightness Kauffmann et al. 2003

12. what is the role of environment? increasing density--> the color of the red sequence is almost independent of environment… but the fraction of galaxies in the red sequence vs. the blue cloud is a strong function of local density decreasing luminosity--> u-r (u-r) Balogh et al. 2004

13. the red sequence & color bimodality seen at z=1! rest U-V color also seen in the DEEP2 redshift survey (Willmer et al. in prep) Bell et al. 2003 rest V magnitude (luminosity)

14. in hierarchical models, merger history determines galaxy morphology ‘Milky Way’ galaxy cluster of galaxies

15. Color-magnitude distribution SDSS SAM

16. predicted color distributions are not bimodal -21.5 -20.5 -22.5 black: SDSS purple: SAM -18.5 -19.5

17. model prediction: color-magnitude relation at high redshift rest U-V color colored points meet R<24 COMBO-17 selection criterion rest V magnitude (luminosity)

18. rest U-V color Bell et al. 2003 rest V magnitude (luminosity)

19. models produce enough bright/massive/bulge dominated galaxies -- but they are too blue red: E/S0 blue: S/Irr cyan: merger red: B/T>0.5 blue: B/T<0.5 cyan: tmrg < 0.5 Gyr GEMS

20. not enough EROs 13.5 5.8 3.2 1.0 0.5 0.1 KAB<22 GOODS rss et al. 2004 GOODS ApJL

21. Bell et al 2003 Results from state-of-the-art numerical hydrodynamic simulations are very similar Dave et al., see also Nagamine et al.

22. Why are red galaxies red? • CDM models produce enough old, massive galaxies. the problem is a continuous ‘trickle’ of star formation • there must be some process that shuts off star formation after galaxies have become massive • this process must be rapid, and seems to be connected with the presence of a spheroid • must work in all environments, but happen to a larger fraction of galaxies in dense places

23. toy models • remove all remaining gas after major mergers • shut off cooling/SF when Mh>Mcrit • shut off star formation when M*>Mcrit • shut off star formation when M*,bulge>Mcrit

24. toy models • remove all remaining gas after major mergers • has almost no effect (fresh gas gets accreted) • shut off cooling/SF when Mh>Mcrit • kills massive galaxies entirely; does not produce bimodality • shut off star formation when M*>Mcrit • kills massive galaxies entirely; does not produce bimodality • shut off star formation when M*,bulge>Mcrit

25. Color-magnitude distribution SDSS SAM: SF shut off when Mh>Mcrit

26. Color-magnitude distribution SDSS SAM: SF shut off when Mbulge>Mcrit

27. Metallicity normalization increased by a factor of 2 SDSS SAM: SF shut off when Mbulge>Mcrit

28. SF quenched when Mbulge>Mcrit Mr<-22.75 (purple=SAM black=SDSS) -21.75 -20.75 -19.75 -18.75

29. when do galaxies become ‘quenched’? SF quenched when Mbulge>Mcrit

30. Mbulge quenched model dry mergers? GEMS

31. AGN: the missing link? • tight observed relation between Mbulge and MBH • energy emitted expected to be proportional to MBH Di Matteo, Springel & Hernquist 2005

32. AGN feedback by momentum-driven winds SDSS ‘transition mass’ Murray, Quataert & Thompson 2004 bulge fg=0.1 fg=0.05 BH observed MBH-s rln

33. ‘momentum wind’ model cold gas ejected (and never re-accreted) if Mbulge>Mcrit(s) still have a ‘cooling flow’ problem!

34. -22.75 AGN‘momentum wind’ model red sequence improved, and bimodality appears in the right place, but too many intermediate luminosity blues… still have a ‘cooling flow’ problem -18.75

35. AGN-feedback model too much scatter in red sequence at high redshift…formation time too late or too spread out

36. AGN feedback model too much scatter in red sequence at high redshift…formation time too late or too spread out

37. ‘Effervescent’ heating by giant radio jets • recent work suggests even columnated jets can heat a large filling factor of ICM • resulting bubbles look similar to those seen in Chandra images of some clusters • Effective in cluster or perhaps group environments Bruggen, Ruszkowski & Hallen 2005

38. Stellar Populations as fossil relics of star formation 10 realizations of a ‘Coma’ cluster

39. ‘real’ vs. ‘grid-derived’ age and metallicity Z from grids age from grids actual light-weighted age actual metallicity

40. SAM Coma Trager et al. Coma data

41. Dry mergers: simulations Bell, Naab, McIntosh, rss et al.

42. Dry mergers: GEMS

43. Dry mergers visible for ~250 Myr • every luminous E has had ~0.5-1 dry merger since z~1 • in good agreement with expectations from hierarchical models

44. Summary • CDM-based models of galaxy formation that produce reasonable agreement with the z=0 stellar mass function form enough massive galaxies at high z<2 • But default models do not produce enough massive red galaxies, especially at high redshift, because of continuous low level star formation. need a new process that quenches star formation in massive, bulge-dominated galaxies • momentum-driven winds powered by AGN a promising mechanism…another process needed to solve ‘cooling flow’ problem -- but must make enough massive galaxies at high redshift!