Rik J. Williams, Daniel D. Kelson, John S. Mulchaey, Alan Dressler, Patrick J. McCarthy, Stephen A. Shectman
We present the first measurement of the evolution of the galaxy group stellar
mass function (GrSMF) to redshift z>~1 and low masses (M*>10^12 Msun). Our
results are based on early data from the Carnegie-Spitzer-IMACS (CSI) Survey,
utilizing low-resolution spectra and broadband optical/near-IR photometry to
measure redshifts for a 3.6um selected sample of 37,000 galaxies over a 5.3
deg^2 area to z~1.2. Employing a standard friends-of-friends algorithm for all
galaxies more massive than log(M*/Msun)=10.5, we find a total of ~4000 groups.
Correcting for spectroscopic incompleteness (including slit collisions), we
build cumulative stellar mass functions for these groups in redshift bins at
z>0.35, comparing to the z=0 and z>0 mass functions from various group and
cluster samples. Our derived mass functions match up well with z>0.35 X-ray
selected clusters, and strong evolution is evident at all masses over the past
8 Gyr. Given the already low level of star formation activity in galaxies at
these masses, we therefore attribute most of the observed growth in the GrSMF
to group-group and group-galaxy mergers, in accordance with qualitative notions
of hierarchical structure formation. Given the factor 3-10 increase in the
number density of groups and clusters with M*>10^12 Msun since z=1 and the
strong anticorrelation between star formation activity and environmental
density, this late-time growth in group-sized halos may therefore be an
important contributor to the structural and star-formation evolution of massive
galaxies over the past 8 Gyr.
View original:
http://arxiv.org/abs/1201.1009
No comments:
Post a Comment