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

Tracy Webb, Pieter van Dokkum, Eiichi Egami, Giovanni Fazio, Marijn Franx, Eric Gawiser, David Herrera, Jiasheng Huang, Ivo Labbe, Paulina Lira, Danilo Marchesini, Jose Maza, Ryan Quadri, Gregory Rudnick, Paul van der Werf

astro-pharXiv:astro-ph/0511598

Abstract

We present Spitzer 24micron imaging of 1.5 < z < 2.5 Distant Red Galaxies (DRGs) in the 10arcmin by 10arcmin Extended Hubble Deep Field South of the Multiwavelength Survey by Yale-Chile. We detect 65% of the DRGs with KAB < 23.2 mag at S24micron > 40uJy, and conclude that the bulk of the DRG population are dusty active galaxies. A mid-infrared (MIR) color analysis with IRAC data suggests that the MIR fluxes are not dominated by buried AGN, and we interpret the high detection rate as evidence for a high average star formation rate of <SFR> = 130+/-30 M/yr. 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/Mpc3 to our completeness limit of KAB = 22.9 mag

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