AAS 207th Meeting, 8-12 January 2006
Session 52 Galaxy Surveys
Oral, Monday, 2:30-4:00pm, January 9, 2006, Delaware B

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[52.04] The Mass-Dependent Evolution of Field Galaxies

K. Bundy, R. S. Ellis (Caltech), C. J. Conselice (University of Nottingham), M. Cooper (UC Berkeley), B. Weiner (Univeristy of Maryland), J. Taylor (Caltech), C. Willmer (Lick Observatory), DEEP2 Team

We have used the Wide Field Infrared Camera (WIRC) at Palomar Observatory to secure K-band detections for over 12,000 galaxies with spectroscopic redshifts in the range 0.2 < z < 1.5 from the DEEP2 Redshift Survey. Our sample covers nearly 1.5 square degrees in four fields. Using stellar masses estimated from the multi-band optical+NIR photometry of sample galaxies, we have measured the evolving galaxy stellar mass function and find several results. While the number of intermediate to high mass galaxies has not evolved significantly since z ~1, the number of star forming galaxies in this population has decreased substantially as star formation activity shifts from higher mass galaxies to lower mass galaxies as a function of cosmic time. We quantify this "downsizing" pattern by tracing the evolution of the transitional mass threshold below which the population is dominated by late-type galaxies and above which it is dominated by early-types. Finally, we find evidence that downsizing is accelerated in regions with above-average environmental density.

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