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

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 KAB < 23.2 mag at S24 μm ≳ 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 KAB = 22.9 mag.

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