Spitzer Observations of Z∼3 Lyman Break Galaxies: Stellar Masses and Mid-infrared Properties

We describe the spectral energy distributions (SEDs) of Lyman Break Galaxies (LBGs) at z∼3 using deep mid-infrared and optical observations of the Extended Groth Strip, obtained with IRAC and MIPS on board Spitzer and from the ground, respectively. We focus on LBGs with detections at all four IRAC bands, in particular the 26 galaxies with IRAC 8 μm band (rest–frame K-band) detections. We use stellar population synthesis models and probe the stellar content of these galaxies. Based on best–fit continuous star-formation models we derive estimates of the stellar mass for these LBGs. As in previous studies, we find that a fraction of LBGs have very red colors and large estimated stellar masses (M∗ > 5× 10 10 M⊙): the present Spitzer data allow us, for the first time, to study these massive LBGs in detail. We discuss the link between these LBGs and submm-luminous galaxies. We find that the number density of these massive LBGs at high redshift is higher than predicted by current semi-analytic models of galaxy evolution. Subject headings: cosmology: observations — galaxies: evolution — galaxies: high redshift — galaxies: stellar content — infrared: galaxies Department of Astrophysics, Oxford University, Keble Rd, Oxford, OX1 3RH, U.K. Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 Steward Observatory, University of Arizona, Tucson, AZ 85721 Joint Center for Astrophysics, Shanghai Normal University, Shanghai 200234, China Shanghai Astronomical Observatory, Chinese Academy of Sciences, Shanghai 200030, China California Institute of Technology, MS 105-24, 1201 E. California, Pasadena, CA 91125 Spitzer Science Center, Caltech, 1200 E. California, Pasadena, CA 91125 Spitzer Fellow