Star Formation in Distant Red Galaxies: Spitzer Observations in the Hubble Deep Field-South

Abstract

We present Spitzer 24 μm imaging of 1.5 < z < 2.5 distant red galaxies (DRGs) in the 10′ × 10′ extended Hubble Deep Field-South of the Multiwavelength Survey by Yale-Chile. We detect 65% of the DRGs with K AB < 23.2 mag at S 24μm ≳ 40 μJy and conclude that the bulk of the DRG population is dusty active galaxies. A mid-infrared (MIR) color analysis with IRAC data suggests that the MIR fluxes are not dominated by buried AGNs, and we interpret the high detection rate as evidence for a high average star formation rate of (SFR) = 130 ±30 M⊙ yr -1 . From this, we infer that DRGs are important contributors to the cosmic star formation rate density at z ∼ 2, at a level of ∼0.02 M⊙ yr -1 Mpc -3 to our completeness limit of K AB = 22.9 mag. © 2006. The American Astronomical Society. All rights reserved.