The Mass Assembly History of Field Galaxies:Detection of an Evolving Mass Limit for Star-Forming Galaxies Submitted to ApJ, astro-ph/0512465 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
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
Downsizing In Observations Surveys to z < 2: Cowie et al. 1996, Brinchmann & Ellis 2000, Bell et al. 2005 COMBO17, Bauer et al. 2005, Juneau et al. 2005, … Higher SFR Treu et al. 2005 Other methods: Treu et al. 2005, van der Wel et al. 2005, Heavens et al. 2005, Jimenez et al. 2005, … Juneau et al. 2005
Downsizing in Theory Simulated Disk Merger with AGN Feedback Galaxy Transformation: Mergers fuel AGN which expel gas and prevent further star formation. Springel et al. 2004 Partial Solution: AGN feedback The fundamental problem… Downsizing Threshold age But, merging is hierarchical, driven by DM assembly. Redshift z (Croton et al 2005) Kevin Bundy, Caltech
Possible Explanations Local Environment: Massive galaxies live in dense environments that mature more rapidly: ram pressure stripping, encounters, harassment. Internal Physics: Physical processes (AGN, SF) within galaxies depend on both mass and redshift.
The DEEP2 Redshift + Palomar K-band Survey GOAL: Chart galaxy evolution as a function of M* over a wide range of environments • DEEP2: 40,000 spec-z’s from DEIMOS on Keck II 80 Keck nights, z<1.5 over 3 deg2, R < 24.1 Spread over 4 fields, including the EGS • Palomar K-band: 65 nights with WIRC on 200 inch 1.5 deg2 to K=20, 0.2 deg2 to K=21 • Combined: 12,000 redshifts with K-band detections
Key Physical Properties • SFR Indicator • (U-B) Restframe Color, C. Willmer • [OII] Equivalent Width, B. Weiner • Morphology (from GOODS, Bundy et al. 2005) • Stellar Mass • Palomar K-band, multi-band SED fitting • Environmental Density • 3rd nearest neighbor, M. Cooper Spectroscopic Redshifts and IR are essential
Results:Galaxy Stellar Mass Function Partitioned by restframe (U-B) color into blue (active) and red (quiescent) populations. Number Density • Little total evolution Mass
Results:Galaxy Stellar Mass Function Partitioned by restframe (U-B) color into blue (active) and red (quiescent) populations. Number Density • Little total evolution • Assembly of early-types without dry merging Mass
Results:Galaxy Stellar Mass Function Partitioned by restframe (U-B) color into blue (active) and red (quiescent) populations. Number Density • Little total evolution • Assembly of early-types without dry merging • Evolving transition mass Mass
Assembly of Red, Early-types Increasing abundance Mass
Assembly of Red, Early-types Increasing abundance Mass
Assembly of Red, Early-types Increasing abundance Mass
Assembly of Red, Early-types Possible problems in models >1011 M >1010 M de Lucia et al. 2005 Mass
Key Result: Quenching Threshold Mass Decreasing abundance Mass
Key Result: Quenching Threshold Mass Decreasing abundance Mass
Key Result: Quenching Threshold Mass Decreasing abundance Mass
Key Result: Quenching Threshold Mass Evolution of MQ SF = Tot exp (M*/MQ) Provides key test for downsizing scenarios Mass
Other Indicators of Star Formation
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.
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. 2005 GOODS study. Slower to respond. Not equivalent to color or SFR.
Extreme Environments Extreme Low Density Extreme High Density Second Cut In Environmental Density
Extreme Environments Low Density Mass
Extreme Environments Low Density Mass
Extreme Environments Low/High Density Mass
Extreme Environments Low/High Density • Moderate dependence on density • Downsizing accelerated in dense regions Mass
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 Mtr and MQ • No density dependence in average environments - weak in the extremes • Quenching caused by internal mechanism, possibly AGN? MQ provides constraints
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
