Spitzer Observations of Massive, Red Galaxies at High Redshift

International audienceWe study massive galaxies at z~1-3.5 using HST optical imaging, ground-based near-IR imaging, and Spitzer observations at 3-24 mum. From Ks-selected galaxies in the ~=130 arcmin2 GOODS-S field, we identify 153 distant red galaxies (DRGs) with (J-Ks)Vega>=2.3. This sample is approximately complete in stellar mass for passively evolving galaxies above 1011 Msolar and z~4-6 mag) starbursts (at zmed~1.7). Very few DRGs (=1011 Msolar have specific star formation rates (SFRs per unit mass) including the reradiated far-IR emission that range from 0.2 to 10 Gyr-1. Based on the X-ray luminosities and rest-frame near-IR colors, roughly one-quarter of the DRGs contain AGNs, implying that the growth of supermassive black holes coincides with the formation of massive galaxies. At 1.5=1011 Msolar have an integrated specific SFR less than the global value and more than an order of magnitude lower than that for massive DRGs. At