Eight billion years of galaxy evolution Eric Bell Borch, Zheng, Wolf, Papovich, Le Floc’h, & COMBO-17, MIPS, and GEMS teams Venice

Eric BellVenice Demographics of the evolving galaxy population Where is the mass?

Eric BellVenice Some demographics A bimodal galaxy population A bimodal galaxy population Red sequence Red sequence Non-star-forming Non-star-forming ~ color of ancient stars ~ color of ancient stars Blue cloud Blue cloud Star-forming Star-forming Absolute magnitude in i-band Blanton et al. 2003; ApJ, 594, 186

Eric BellVenice Evolution I Labbé et al (M 2200 – V) rest MVMVMVMV Always a blue cloud Emergence of the red sequence -Some massive galaxies at all times… z ~ 1 z ~ 1.8 z ~ 2.6

Eric BellVenice Evolution II Evolution II Bell et al. 2004

Eric BellVenice Mass function: color split Borch et al Local MFs Weak evolution in blue guys (~ disks) Strong evolution in red guys at L<2L* at least (~ spheroids) Blue cloud Red sequence Bundy et al. 2006

Eric BellVenice Evolution IV Always a pronounced blue cloud Always a pronounced blue cloud Color redder with time Color redder with time Red sequence builds up with time Red sequence builds up with time Color of ancient stars at every epoch 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; Blanton 2006; Bundy et al. 2006) Build-up of x3 or so since z~1 (Bell et al. 2004; Chen et al. 2003; Willmer, Faber et al. 2006; Blanton 2006; Bundy et al. 2006) In agreement with at least some models (Cole et al. 00; Somerville et al. in prep) In agreement with at least some models (Cole et al. 00; Somerville et al. in prep) Chen et al. 03 Borch et al Blue cloud Red sequence Bundy et al. 2006

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

Eric BellVenice Demographics of the evolving galaxy population Where is the star formation?

Eric BellVenice Cosmic SFR UV / IR / radio / emission lines UV / IR / radio / emission lines Luminosity function extrapolation a challenge Luminosity function extrapolation a challenge Reasonable agreement Reasonable agreement Hopkins 2004

Eric BellVenice Which galaxies form stars? Red E/S0s are non-star-forming Red E/S0s are non-star-forming Most SF is in spiral galaxies Most SF is in spiral galaxies Rest-frame V-band absolute magnitude Rest-frame U-V E/S0Sa—Sd Irr/compact Clearly interacting Bell et al Melbourne, Koo & Le Floc’h Log L IR log Φ -3

Eric BellVenice Spitzer: new insights 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 (Kroupa IMF ~ 0.5x Salpeter) 83μJy limit corresponding to 3M  yr -1 at z~0.7 (Kroupa IMF ~ 0.5x Salpeter) Spitzer image COMBO-17 and GEMS coverage Rieke et al. 2004; data described in Papovich et al. 2004

Eric BellVenice IR luminosity from 24μm flux Rest-frame 12-15μm correlates strongly with total IR luminosity in the local Universe, with < x2 scatter Rest-frame 12-15μm correlates strongly with total IR luminosity in the local Universe, with < x2 scatter Will be able to test IR flux estimates with Spitzer 70,160μm, Apex 350μm and 870μm and Herschel PACS and SPIRE Will be able to test IR flux estimates with Spitzer 70,160μm, Apex 350μm and 870μm and Herschel PACS and SPIRE Chary & Elbaz 2001; Papovich & Bell 2002; See also Dale et al Log 10 L IR /L  Log 10 ν L ν,15μm /L  <0.3 dex scatter

Eric BellVenice Evolution of IR LF IR LF very strongly evolving Almost all SF is in blue disks Total Blue / disk Local Red Le Floc’h et al Bell et al. 2005

Eric BellVenice Split by color Can compare integrated SFR with observed mass growth: IR- derived Can compare integrated SFR with observed mass growth: IR- derived Blue disks form stars Blue disks form stars Stars end up in red spheroid- dominated galaxies Stars end up in red spheroid- dominated galaxies Bell et al., in prep., Le Floc’h et al. 2005

Eric BellVenice The evolution of the mass function… Can estimate evolution of the mass function with time Can estimate evolution of the mass function with time t t+dt For each mass bin: Work out average dM*/dt - stacking  average SFR - stacking  average SFR Multiply by Δt to work out ΔM*

Eric BellVenice Results Hypothesis 1: SF in red  red Hypothesis 1: SF in red  red SF in blue  blue SF in blue  blue log space density log stellar mass All galaxies Red galaxies Blue galaxies z = Obs. MF Pred. MF

Eric BellVenice Results Hypothesis 1: All SF  red Hypothesis 1: All SF  red log space density log stellar mass All galaxies Red galaxies Blue galaxies z = Obs. MF Pred. MF

Eric BellVenice The role of mergers Merger rates Merger rates Morphologically- messed up things Morphologically- messed up things Close galaxy pairs Close galaxy pairs Neither are perfect Neither are perfect Patton et al Bundy et al Le Fevre et al Conselice et al Somerville et al. in prep. * Bell et al. 06

Eric BellVenice The role of mergers Merger rates Merger rates Morphologically- messed up things Morphologically- messed up things Close galaxy pairs Close galaxy pairs Neither are perfect Neither are perfect Current estimates suggest ~1/3 merger per L* galaxy Current estimates suggest ~1/3 merger per L* galaxy Patton et al Bundy et al Le Fevre et al Conselice et al Somerville et al. in prep. * Bell et al. 06

Eric BellVenice Conclusions Galaxies come in 2 flavours Galaxies come in 2 flavours Blue Blue Star-forming (often very intense) Star-forming (often very intense) Disk-dominated Disk-dominated Food for the red sequence Food for the red sequence Red Red Largely non-star-forming Largely non-star-forming Bulge-dominated Bulge-dominated Constant growth of red population through global suppression of SF in blue guys Constant growth of red population through global suppression of SF in blue guys Physical mechanisms of suppression Physical mechanisms of suppression Environment Environment Gas consumption Gas consumption Mergers Mergers ~1/3 merger per L* galaxy ~1/3 merger per L* galaxy

Eric BellVenice SFR vs. SFH Borch et al. 2006

Eric BellVenice Always a pronounced blue cloud Always a pronounced blue cloud Color redder with time Color redder with time Red sequence builds up with time Red sequence builds up with time Color of ancient stars at every epoch Color of ancient stars at every epoch Evolution III Faber, Willmer, Wolf et al Passive evolution See also Bell et al. 2004