Specific Star Formation Rates

Abstract

We present results from a study to determine how star formation contributes to galaxy growth since redshift z=1.5. Using galaxies from the MUnich Near-Infrared Cluster Survey (MUNICS) and the FORS Deep Field (FDF), we investigate the specific star formation rate (SSFR, star formation rate [SFR] per unit galaxy stellar mass) as a function of galaxy stellar mass and redshift. We test the compatibility of our results with a sample drawn from a larger volume using the Sloan Digital Sky Survey. We find that the SSFR decreases as galaxy stellar mass increases, suggesting that star formation contributes more to the growth of low-mass galaxies than high-mass galaxies at all redshifts in this study. We also find a ridge in the SSFR that runs parallel to lines of constant SFR and decreases by a factor of 10 from z=1 to today, matching the results of the evolution in SFR density seen in the ``Lilly-Madau'' diagram. The ridge evolves independently of galaxy stellar mass to a particular turnover mass at the high mass end. Galaxies above the turnover mass show a sharp decrease in SSFR compared to the average at that epoch, and the turnover mass increases with redshift.