The Density and Spectral Energy Distributions of Red Galaxies at Z ∼ 3.7

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/4000 Å breaks at 2 < z < 4.5. Analagous to the J−K > 1.3 (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 < z < 3 and 3 < z < 4.5, respectively. From the FIRES catalogs of the HDF-S (4.7 arcmin) and MS 1054-03 (26.3 arcmin) fields, we find 18 galaxies with 〈zphot〉 = 2.4 that satisfy Js −H > 0.9;H < 23.4 and 23 galaxies with 〈zphot〉 = 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 ± 0.5 × 10 −4 and 1.2 ± 0.4× 10 Mpc, 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-redshiftH−Ks selected sample have blue NUV-optical colors and UV slopes similar to those of Lyman Break Galaxies, while the Js −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 〈AV 〉JH = 1 mag and 〈AV 〉HK = 0.2 mag. 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. Subject headings: cosmology: observations — galaxies: evolution — galaxies: formation