Specific Star Formation Rates to Redshift 1.5

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  • 15 December 2004
Abstract
We present a study to determine how star formation contributes to galaxy growth since z=1.5 over five decades in galaxy stellar mass. We investigate the specific star formation rate (SSFR, star formation rate per unit galaxy stellar mass) as a function of galaxy stellar mass and redshift. A sample of 175 K-band selected galaxies from the MUNICS spectroscopic dataset provide intermediate to high mass galaxies (mostly M* > 10^10 Msun) to z=1. The FORS Deep Field provides 168 low mass galaxies (mostly M* < 10^10 Msun) to z=1.5. We use an SDSS galaxy sample to test the compatibility of our results with data drawn from a larger volume. We find that at all redshifts, the specific star formation rate decreases with increasing galaxy stellar mass suggesting that star formation contributes more to the growth of low mass galaxies than to the growth of high mass galaxies, and that high mass galaxies formed the bulk of their stellar content before z=1. At each epoch we find a ridge in SSFR versus stellar mass that is parallel to lines of constant star formation rate and evolves independent of galaxy stellar mass to a particular turnover mass. Galaxies above this turnover mass show a sharp decrease in SFR compared to the average at each epoch and the turnover mass increases with redshift. The SFR along the SSFR ridge decreases by roughly a factor of 10, from 10 Msun/yr at z=1.5 to 1 Msun/yr at z=0. High mass galaxies could sustain the observed rates of star formation over the 10 Gyrs observed, but low mass galaxies likely undergo episodic starbursts.

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