Kevin Bundy, Caltech The Mass Assembly History of Field Galaxies: Detection of an Evolving Mass Limit for Star-Forming Galaxies Kevin Bundy R. S. Ellis, C. J. Conselice, J. Taylor, M. Cooper, C. Willmer, B. Weiner, P. Eisenhardt, K. Noeske, A. Coil, DEEP2 Team Galaxies and Structures through Cosmic Time, Venice March 2006 Submitted to ApJ, astro-ph/

Kevin Bundy, Caltech Downsizing In Words The sites of active star formation shift from high-mass galaxies at early epochs (z~1-2) to low-mass galaxies as a function of cosmic time. Term coined by Cowie et al. 1996

Kevin Bundy, Caltech Downsizing In Observations Surveys to z < 2 : Cowie et al. 1996, Brinchmann & Ellis 2000, Bell et al COMBO17, Bauer et al. 2005, Juneau et al. 2005, … Juneau et al Treu et al Other methods : Treu et al. 2005, van der Wel et al. 2005, Heavens et al. 2005, Jimenez et al. 2005, … Higher SFR

Kevin Bundy, Caltech Downsizing in Theory Kevin Bundy, Caltech Galaxy Transformation: Mergers fuel AGN which expel gas and prevent further star formation. But, merging is hierarchical, driven by DM assembly. Redshift z Downsizing Threshold Springel et al Simulated Disk Merger with AGN Feedback age Partial Solution: AGN feedback (Croton et al 2005) The fundamental problem…

Kevin Bundy, Caltech Possible Explanations 1. Local Environment: Massive galaxies live in dense environments that mature more rapidly: ram pressure stripping, encounters, harassment. 2. Internal Physics: Physical processes (AGN, SF) within galaxies depend on both mass and redshift.

Kevin Bundy, Caltech The DEEP2 Redshift + Palomar K-band Survey DEEP2: 40,000 spec-z’s from DEIMOS on Keck II 80 Keck nights, z<1.5 over 3 deg 2, R < 24.1 Spread over 4 fields, including the EGS Palomar K-band: 65 nights with WIRC on 200 inch 1.5 deg 2 to K=20, 0.2 deg 2 to K=21 Combined: 12,000 redshifts with K-band detections GOAL: Chart galaxy evolution as a function of M * over a wide range of environments

Kevin Bundy, Caltech Key Physical Properties 1. SFR Indicator (U-B) Restframe Color, C. Willmer [OII] Equivalent Width, B. Weiner Morphology (from GOODS, Bundy et al ) 2. Stellar Mass Palomar K-band, multi-band SED fitting 3. Environmental Density 3 rd nearest neighbor, M. Cooper Spectroscopic Redshifts and IR are essential

Kevin Bundy, Caltech Results: Galaxy Stellar Mass Function Partitioned by restframe (U-B) color into blue (active) and red (quiescent) populations. Mass Number Density Little total evolution

Kevin Bundy, Caltech Results: Galaxy Stellar Mass Function Partitioned by restframe (U-B) color into blue (active) and red (quiescent) populations. Mass Little total evolution Assembly of early- types without dry merging Number Density

Kevin Bundy, Caltech Results: Galaxy Stellar Mass Function Partitioned by restframe (U-B) color into blue (active) and red (quiescent) populations. Mass Little total evolution Assembly of early- types without dry merging Evolving transition mass Number Density

Kevin Bundy, Caltech Assembly of Red, Early-types Mass Increasing abundance

Kevin Bundy, Caltech Assembly of Red, Early-types Mass Increasing abundance

Kevin Bundy, Caltech Assembly of Red, Early-types Mass Increasing abundance

Kevin Bundy, Caltech Assembly of Red, Early-types de Lucia et al Possible problems in models Mass >10 10 M  >10 11 M 

Kevin Bundy, Caltech Mass Key Result: Quenching Threshold Mass Decreasing abundance

Kevin Bundy, Caltech Mass Key Result: Quenching Threshold Mass Decreasing abundance

Kevin Bundy, Caltech Mass Key Result: Quenching Threshold Mass Decreasing abundance

Kevin Bundy, Caltech Evolution of M Q  SF =  Tot exp (M * /M Q ) Key Result: Quenching Threshold Mass Mass Provides key test for downsizing scenarios

Kevin Bundy, Caltech Other Indicators of Star Formation

Kevin Bundy, Caltech Other Indicators of Star Formation SF cut is median of mid-z bin. More stringent so more early types, fewer late. SF increases in high-z bin.

Kevin Bundy, Caltech Other Indicators of Star Formation SF cut is median of mid-z bin. More stringent so more early types, fewer late. SF increases in high-z bin. Morph from Bundy et al GOODS study. Slower to respond. Not equivalent to color or SFR.

Kevin Bundy, Caltech Extreme Environments Extreme Low Density Extreme High Density Second Cut In Environmental Density

Kevin Bundy, Caltech Extreme Environments Mass Low Density

Kevin Bundy, Caltech Extreme Environments Mass Low Density

Kevin Bundy, Caltech Extreme Environments Mass Low/High Density

Kevin Bundy, Caltech Extreme Environments Mass Moderate dependence on density Downsizing accelerated in dense regions Low/High Density

Kevin Bundy, Caltech Summary & Conclusions Intermediate to high mass galaxies assembled by z~1, but demographics of population changes Early appearance of massive early-types: a continuing problem for models; dry merging not needed Quenching of SF seems to produce downsizing, transformation follows, quantify with M tr and M Q No density dependence in average environments - weak in the extremes Quenching caused by internal mechanism, possibly AGN? M Q provides constraints

Kevin Bundy, Caltech Future Work Probe the mass function at lower masses and higher redshift Study galaxies in the midst of transition: test the merger/AGN scenario directly