SpitzerObservations of Massive, Red Galaxies at High Redshift

We investigate the properties of massive galaxies at z=1-3. 5 using HST observations, ground-based near-IR imaging, and Spitzer Space Telescope observations at 3-24 micron. We identify 153 distant red galaxies (DRGs) with J-K > 2. 3 mag (Vega) in the southern GOODS field. This sample is approximately complete in stellar mass for passively evolving galaxies above 10¹1 solar masses and z 10¹1 solar masses have specific SFRs (SFRs per unit stellar mass) ranging from 0. 2 to 10 Gyr^-1, with a mean value of ~2. 4 Gyr^-1. The DRGs with stellar masses > 10¹1 solar masses and 1. 5 < z < 3 have integrated specific SFRs greater the global value over all galaxies. In contrast, we find that galaxies at z = 0. 3-0. 75 with these stellar masses have integrated specific SFRs less than the global value, and more than an order of magnitude lower than that for massive DRGs at z = 1. 5-3. At z < 1, lower-mass galaxies dominate the overall cosmic mass assembly. This suggests that the bulk of star formation in massive galaxies occurs at early cosmic epochs and is largely complete by z~1. 5. Abridged