1. 9 Gyr of massive galaxy evolution Bell (MPIA), Wolf (Oxford), Papovich (Arizona), McIntosh (UMass), and the COMBO-17, GEMS and MIPS teams Baltimore 27 th September 2004

2. Eric BellBaltimore 27 th Sep 2004 Understanding the physics of galaxy growth The last 9 Gyr has witnessed a strong decline in cosmic- averaged star formation rate…. The last 9 Gyr has witnessed a strong decline in cosmic- averaged star formation rate…. Hopkins 2004

3. Eric BellBaltimore 27 th Sep 2004 COMBO-17 and GEMS… λ [nm] % 3 x ¼ square degree Yields ~ 25000 galaxies with ∂z/(1+z) ~ 0.02; 99% complete GEMS: HST F606W and F850LP mosaic of 28’x28’ – 400 million Independent resolution elements Morpholgies for 10000 galaxies with z<1.1 and optical SEDs Wolf, Meisenheimer, et al. 2003, 2004 R-band apparent magnitude

4. Eric BellBaltimore 27 th Sep 2004 …meet Spitzer! Spitzer 24μm data from the MIPS instrument team for the CDFS Spitzer 24μm data from the MIPS instrument team for the CDFS 83μJy limit corresponding to 3M  yr -1 at z~0.7 83μJy limit corresponding to 3M  yr -1 at z~0.7 Spitzer image COMBO-17 and GEMS coverage

5. Eric BellBaltimore 27 th Sep 2004 Optical vs. IR perspective Morphologically- normal galaxies Morphologically- normal galaxies Red sequence – old, red, dead Red sequence – old, red, dead Blue cloud – star forming Blue cloud – star forming Morphologically- peculiar galaxies Morphologically- peculiar galaxies Optical color no predictor of SFR and SFH Optical color no predictor of SFR and SFH Rest-frame V-band absolute magnitude Rest-frame U-V E/S0Sa—Sd Irr/compact Clearly interacting Bell et al. 2005; submitted to ApJ

6. Eric BellBaltimore 27 th Sep 2004 Under what circumstances does star formation thrive at z~0.7? The bulk of star formation 7 Gyr ago is in morphologically- normal spiral galaxies The bulk of star formation 7 Gyr ago is in morphologically- normal spiral galaxies z~0.7 star formation is not driven by major mergers z~0.7 star formation is not driven by major mergers Star formation driven primarily by quiescent disk evolution or tidal interactions? Star formation driven primarily by quiescent disk evolution or tidal interactions? Bell et al. 2005 submitted to ApJ

7. Eric BellBaltimore 27 th Sep 2004 But, SF in massive galaxies switches off completely in the next 7 Gyr… 1/3 of z~0.7 massive galaxies have SFR/ in excess of 2, cf. 1% in local galaxies. 1/3 of z~0.7 massive galaxies have SFR/ in excess of 2, cf. 1% in local galaxies. log (stellar mass) log (stellar mass) log (stellar mass) log SFR/ log SFR/ Constant SFR Massive starbursts with 2x their past-averaged SFR Bell et al. 2005 submitted to ApJ

8. Eric BellBaltimore 27 th Sep 2004 Recall…. Morphologically- normal galaxies Morphologically- normal galaxies Red sequence – old, red, dead Red sequence – old, red, dead Blue cloud – star forming Blue cloud – star forming Morphologically- peculiar galaxies Morphologically- peculiar galaxies Optical color no predictor of SFR and SFH Optical color no predictor of SFR and SFH Rest-frame V-band absolute magnitude Rest-frame U-V E/S0Sa—Sd Irr/compact Clearly interacting Bell et al. 2005; submitted to ApJ

9. Eric BellBaltimore 27 th Sep 2004 B-band LF of red-sequence Red sequence luminosity function evolution Red sequence luminosity function evolution Essentially passive M* evolution Essentially passive M* evolution Increase in Φ* towards the present Increase in Φ* towards the present Rest-frame B-band absolute magnitude Comoving Space Density Bell et al. 2004

10. Eric BellBaltimore 27 th Sep 2004 Studying suppression of SF through red sequence evolution Non-evolving B-band luminosity density evolution + Essentially passive color evolution

11. Eric BellBaltimore 27 th Sep 2004 The slow build-up of old, red and dead galaxies  Half of the stellar mass in present-day old, red and dead galaxies was in star-forming galaxies 9 Gyr ago…  Half of the stellar mass in present-day old, red and dead galaxies was in star-forming galaxies 9 Gyr ago… Cole et al. 2000 semi-analytic galaxy formation model Passive evolution Stellar mass density Redshift

12. Eric BellBaltimore 27 th Sep 2004 Gaining insight from evolution as a function of environment The relative rate of increase in old, red and dead galaxies is faster in low-density environments  The physical processes which dominate the turning off of star formation in the last 9 Gyr are those which operate in low-density environments (e.g., gas consumption or galaxy merging) M V < -20 Low density All galaxies Redshift Red galaxy fraction High density Bell et al. in prep.

13. Eric BellBaltimore 27 th Sep 2004 Conclusions Intense star formation at z~0.7, predominantly in spirals with ~20% from interactions… Intense star formation at z~0.7, predominantly in spirals with ~20% from interactions… Clear evidence for galaxy-wide suppression of star formation in an increasingly large fraction of galaxies; these processes operate in primarily in the field with some cluster contributions Clear evidence for galaxy-wide suppression of star formation in an increasingly large fraction of galaxies; these processes operate in primarily in the field with some cluster contributions What turns galaxies on What turns galaxies on being left alone, and perhaps weak interactions being left alone, and perhaps weak interactions Strong interactions are exciting for a brief time… Strong interactions are exciting for a brief time… What turns galaxies off What turns galaxies off Mostly field processes, such as running out of gas or major mergers Mostly field processes, such as running out of gas or major mergers

14. Eric BellBaltimore 27 th Sep 2004 Not quite old, red, and dead Yi et al 2004; ApJL in press

15. Eric BellBaltimore 27 th Sep 2004 In which environments are the early-type galaxies evolving? Springel, Yoshida & White 2001 & White 2001

16. Eric BellBaltimore 27 th Sep 2004 Environments with photozs High density Low density

17. Eric BellBaltimore 27 th Sep 2004 Gaining insight from evolution as a function of environment The relative rate of increase in old, red and dead galaxies is faster in low-density environments  The physical processes which dominate the turning off of star formation in the last 9 Gyr are those which operate in low-density environments (e.g., gas consumption or galaxy merging) M V < -20 Low density All galaxies Redshift Red galaxy fraction High density Bell et al. in prep.

18. Eric BellBaltimore 27 th Sep 2004 Red galaxy fraction evolution in different environments Minimal field evolution consistent with the observed evolution Can rule out non-evolving f red in the field… But, later formation of field red sequence is not required by the data Red galaxy fraction Redshift

19. Eric BellBaltimore 27 th Sep 2004 Morphologies at z~0.75 split by environment from GEMS Low-density environment High-density environment Spheroid-dominatedDisk-dominated 30% of early-types blue 50% of early-types blue  Consistent with later addition of early-type population in lower density environments…