Carnegie-Spitzer-IMACS Survey: The Rise of Galaxy Groups Since z=1
Abstract
We present the first measurements of the evolution of the group stellar mass function (GSMF) since z=1 from the Carnegie-Spitzer-IMACS (CSI) Survey. CSI combines robust mass selection through Spitzer 3.6-micron photometry with low-resolution spectroscopy over a 15 deg2 area, allowing the detailed study of large group (and group/field galaxy) samples over the expected epoch of group formation. From the initial 36,000 CSI galaxy redshifts over 5 deg2, we select groups using a standard friends-of-friends algorithm in angular and redshift space, constructing the GSMF in 3 redshift bins. These mass functions agree well with GSMFs from SDSS at z=0, and with X-ray-selected cluster mass functions at higher masses and redshifts. At all masses the GSMF evolves strongly from z=0.5-1, but only weak evolution is seen in low-mass (log M* ∼ 12.0) groups since z=0.5, indicating that most of these were in place at that epoch. As the majority of low-redshift galaxies reside in groups, the group environment may therefore play an important role in the decline in star formation and evolution of galaxy structures since z=1.
- Publication:
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American Astronomical Society Meeting Abstracts #219
- Pub Date:
- January 2012
- Bibcode:
- 2012AAS...21922904W