Galaxy Evolution

1. Galaxy Evolution Galaxies Block Course March 09 Eric Bell

2. The Evolution of the Cosmic Star Formation Rate • When did it start / ramp up? • When were half of the stars formed? • Can it be understood (in terms of models)? • When/how did the first stars form? • Estimating the “cosmic star-formation rate” • Estimating the SFRs in individual objects • Are all relevant sources included • Faint • Obscured Galaxies Block Course March 09 Eric Bell

3. SFR vs. SFH Borch et al. 2006 Galaxies Block Course March 09 Eric Bell

4. Modeling/interpreting the <SFR>(z) • The <SFR> = f(z,Mhalo) is a consequence of • Fluctuation/halo growth • Gas cooling in those halos (cold fuel supply) • [feed-back] • Simulation approaches • Direct cosmological hydro-dynamical simulations (e.g. Springel and Hernquist 2005) • Main issues: resolution + star-formation (+feedback ‘recipe’) • Semi-analytic models (Kauffmann; Lacey and Cole ’93  Croton et al 06, Somerville et al 08) • DM halo abundance and merging from Press-Schechter Theo. • Main issues: galaxy merging, spatial information, + star-formation (+feedback ‘recipe’) Galaxies Block Course March 09 Eric Bell

5. Elements of the Modelling • http://www.daf.on.br/etelles/lectures/lacey-2.pdf Galaxies Block Course March 09 Eric Bell

6. Galaxies Block Course March 09 Eric Bell

7. Galaxies Block Course March 09 Eric Bell

8. Galaxies Block Course March 09 Eric Bell

9. Results of such simulations1st example: Springel & Hernquist 03 Different assumptions  different <SFR>(z) No feed-back  stars for too early (and too many of them) There are plausible (not unique) approaches to SF and feed-back descriptions that match <SFR>(z) Galaxies Block Course March 09 Eric Bell

10. Comparison data—models(Somerville et al 08) No feed-back  vast overprediction of stars at all halo masses No AGN feed-back  overprediction of stars at HIGH halo masses Log(fraction) of baryons that have ended up (at z~0) as stars in halos of mass Mhalo Observational constraint (from B. Moster) Galaxies Block Course March 09 Eric Bell

11. Now .. How did star-formation start at all in the cosmos?(Tom Abel, Greg Bryant, Volker Bromm etc..) Galaxies Block Course March 09 Eric Bell

12. Galaxies Block Course March 09 Eric Bell

13. Predictions I • Almost all galaxies have gas cooling --> star formation… • Davé et al. • Natural state of all galaxies is to form stars… Galaxies Block Course March 09 Eric Bell

14. Predictions II Dynamical assembly history - a probe largely of DM and baryons = disks, conservation AM = spheroids, mergers/int Matthias Steinmetz, AIP Galaxies Block Course March 09 Eric Bell

15. What does the Universe really do? Galaxies Block Course March 09 Eric Bell

16. Observation • Blanton+03 • Strong bimodality in color-magnitude relation Galaxies Block Course March 09 Eric Bell

17. Observation • Bimodality in color space --> narrow distribution in SFR/M* (blue galaxies) with tail towards low SFR/M* (red sequence) • Schiminovich+ 2008 Galaxies Block Course March 09 Eric Bell

18. Key observation : correlation between structure and star formation history Blanton et al. 2003; ApJ, 594, 186 • A bimodal galaxy population - transition mass of 3e10 • Red sequence • Mostly non-star-forming • Bulk of galaxies bulge-dominated • Most massive galaxies • Blue cloud • Star-forming • Bulk of galaxies disk-dominated • Lower mass galaxies Blue, forms starsRed, non SF Low mass High mass -18 -20 -22 Absolute magnitude in i-band Cessation (quenching) of star formation is empirically correlated with the existence of a prominent spheroid Galaxies Block Course March 09 Eric Bell

19. Red correlates with environment… Mean overdensity Mean overdensity Galaxies Block Course March 09 Eric Bell

20. Story so far… • Cooling/SF/stellar feedback cannot make a red sequence • 1/2 of all stellar mass today! • Primarily concentrated spheroidal galaxies • Correlated also with environment… Galaxies Block Course March 09 Eric Bell

21. Spheroids vs. black holes… Black hole mass- bulge mass correlation Scatter <0.3 dex Possibility of a link between bulge formation and BH formation Häring and Rix 2004 Galaxies Block Course March 09 Eric Bell

22. Story so far… • Cooling/SF/stellar feedback cannot make a red sequence • 1/2 of all stellar mass today! • Primarily concentrated spheroidal galaxies • Because of black holes? • AGN feedback? • Correlated also with environment… Galaxies Block Course March 09 Eric Bell

23. Some empirical progress… • Study how red sequence evolves • Try to split structure vs. environment • Is a bulge an absolute requirement for shutting off star formation? Galaxies Block Course March 09 Eric Bell

24. Evolution of the red sequence Galaxies Block Course March 09 Eric Bell

25. Evolution of red sequence z=1 to today… Bell et al. 2004 Galaxies Block Course March 09 Eric Bell

26. Mass function: color split Blue cloud Local MFs Red sequence Weak evolution in blue guys (= disks) Strong evolution in red guys at L<2L* at least (= spheroids) Borch et al. 2006 Galaxies Block Course March 09 Eric Bell

27. Stellar mass density red/blue Borch et al. 2006 • Always a pronounced blue cloud • Color redder with time • Red sequence builds up with time • Color of ancient stars at every epoch • Build-up of x3 or so since z~1 (Bell et al. 2004; Chen et al. 2003; Willmer, Faber et al. 2006) • In agreement with at least some models (Cole et al. 00; Somerville et al. 2008) Red sequence Chen et al. 03 Blue cloud Galaxies Block Course March 09 Eric Bell

28. Where’s the mass? • A red sequence • Dominated by spheroids at z<1 • Color evolves ~ passively •  stellar mass density increases by x2 or more • Most mass is in spheroids at redshifts below ~0.7 • A blue cloud • Dominated by disks • Color reddens towards present day • Stellar mass function more or less constant since z~1 Galaxies Block Course March 09 Eric Bell

29. Environment? • g-r vs. stellar mass • Weakly dependent on halo mass (bottom panel) • Weakly dependent on radius (centre panel) • Stellar mass is a much more important driver of properties than halo mass • Weak residual trend towards redness for more massive clusters (small radii) Van den Bosch et al. 2008 Galaxies Block Course March 09 Eric Bell

30. Bulges A necessary condition for quenching? Galaxies Block Course March 09 Eric Bell

31. Bulges: a necessary condition for quenching? • In AGN feedback paradigm, only way for a central galaxy to stop gas cooling is through AGN feedback • Need bulge • Are there any red central galaxies without bulges? Galaxies Block Course March 09 Eric Bell

32. SDSS DR2 NYU VAGC Blanton+05 Group catalog Yang et al 05 SF/AGN Brinchmann+04 Bell 2008 Galaxies Block Course March 09 Eric Bell

33. Galaxies Block Course March 09 Eric Bell

34. Galaxies Block Course March 09 Eric Bell

35. Bulge (SMBH) requirement for quenching for central galaxies Many red sequence n<1.5 have AGN * Internally- driven transform Sd-Im to Sph unlikely (predict all Sph satellites) Galaxies Block Course March 09 Eric Bell

36. Closing remarks What does this all mean? Galaxies Block Course March 09 Eric Bell

37. Summary • Halo formation, cooling, star formation and stellar feedback • Star forming galaxies • Mix of spheroid-dominated and disk-dominated • Observations • Almost all spheroid-dominated galaxies are red, non-star-formers • Not primarily environmental • Bulge is a necessary but not sufficient condition for quenching; suggests AGN feedback Galaxies Block Course March 09 Eric Bell

38. Can AGN feedback work in practice? • Implementation in models • Quasar mode (Kauffmann & Haehnelt 2000) • Powerful outflow evacutes gas and quenches star formation immediately (not clear required by observations) • Radio mode (Croton et al. 2006) • Heating of hot gas envelope of galaxies stops further gas cooling • Very successful qualitatively • Particularly effective when have hot gas as working surface (Dekel, Cattaneo) • P. Hopkins et al. 2006-present Galaxies Block Course March 09 Eric Bell

39. Quasar mode feedback? • Tremonti et al 2007 find high velocity outflows in post starburst (also post-AGN) systems Galaxies Block Course March 09 Eric Bell

40. Radio mode feedback? • Perseus cluster; bubbles and sound waves associated with hot gas bubbles blown by AGN jets… Fabian et al. Galaxies Block Course March 09 Eric Bell

41. AGN feedback • mergers feed central black hole, giving rise to an ‘Active Galactic Nucleus’ (AGN) • very efficient conversion of rest-mass to energy! • this energy can couple to the cold gas in the galaxy & may drive powerful winds Di Matteo, Springel & Hernquist 2005 Hopkins et al. 2005, 2006 Galaxies Block Course March 09 Eric Bell

42. What happens when we include these processes in a cosmological simulation? AGN feedback suppresses cooling in massive halos z=0 stellar mass function stellar mass supernova-driven winds suppress star formation in low-mass halos host halo mass Galaxies Block Course March 09 Eric Bell

43. models without AGN feedback do not reproduce the slope of the ‘red sequence’ or the color bimodality red dot: spheroid blue dash: disk cyan star: merger GEMS data model Galaxies Block Course March 09 Eric Bell faint bright rss et al. in prep

44. model with AGN feedback: • massive, spheroid dominated galaxies have a • massive BH, which is able to release enough • energy to remove the gas from the galaxy and quench further star formation. GEMS Somerville et al. 2009 Galaxies Block Course March 09 Eric Bell

45. Summary • Halo formation, cooling, star formation and stellar feedback • Star forming galaxies • Mix of spheroid-dominated and disk-dominated • Observations • Almost all spheroid-dominated galaxies are red, non-star-formers • Not primarily environmental • Bulge is a necessary but not sufficient condition for quenching; suggests AGN feedback • Modelling AGN feedback • Quasar mode possibly important • Radio mode is likely to be vital • Qualitative successes, quantitative success is likely far off Galaxies Block Course March 09 Eric Bell