The Density and Spectral Energy Distributions of Red Galaxies at z ~ 3.7

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Abstract
We use the deep NIR imaging of the FIRES survey to investigate trends with redshift of the properties of galaxies selected to have strong Balmer/4000A breaks at 21.3 (AB) color criterion designed to select red galaxies at z>2, we propose two color criteria, J-H>0.9 and H-K>0.9, to select red galaxies in two redshift bins at 2=2.4 that satisfy Js-H>0.9; H=3.7 that satisfy H-Ks>0.9; Ks<24.6, where the flux limits are chosen to match the limiting rest-frame luminosities at the different median redshifts of the two samples. The space densities of the Js-H and H-Ks samples are 1.5+-0.5x10^-4 and 1.2+-0.4x10^-4 Mpc^-3, respectively. The rest-frame U-B colors of galaxies in both samples are similarly red (as expected from the definition of the color criteria), but the rest-frame UV properties are different: galaxies in the higher-redshift H-K selected sample have blue NUV-optical colors and UV slopes similar to those of Lyman Break Galaxies, while the J-H galaxies are generally red over the entire wavelength range observed. Synthetic template fits indicate that the distinct rest-NUV properties of the two samples are primarily a result of dust: we find mean A_V=1 mag (J-H sample) and A_V=0.2 mag (H-K). The median stellar mass determined from the template fits decreases by a factor of ~5 from z=2.4 to 3.7, which, coupled with the fact that the space density of such galaxies remains roughly constant, may imply that the stellar mass density in red galaxies decreases by a similar factor over this redshift range.Comment: 4 pages, 3 figures ; accepted for publication in ApJ Letter
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