Infrared Luminous Lyman Break Galaxies: A Population that Bridges LBGs and SCUBA Galaxies

A deep midand far-infrared survey in the Extended Groth Strip (EGS) area gives 3.6 to 8μm flux densities or upper limits for 253 Lyman Break Galaxies (LBGs). The LBGs are a diverse population but with properties correlated with luminosity. The LBGs show a factor of 30 range in indicated stellar mass and a factor of 10 in apparent dust content relative to stellar mass. About 5% of LBGs are luminous at all wavelengths with powerful emission at rest 6μm. In the rest 0.9 to 2μm spectral range these galaxies have stellar spectral slopes with no sign of an AGN power law component, suggesting that their emission is mainly powered by intensive star formation. Galaxies in this luminous population share the infrared properties of cold SCUBA sources: both are massive and dusty starburst galaxies at 2 < z < 3; their stellar mass is larger than 1011M⊙. We suggest that these galaxies are the progenitors of present-day giant elliptical galaxies, with a substantial fraction of their stars already formed at z ≈ 3. Subject headings: cosmology: observations — galaxies: high redshift — galaxies: Survey — galaxies: mid-infrared Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 Department of Astrophysics, Oxford University, Keble Rd, Oxford, OX1 3RH, U.K. Spitzer Science Center, Caltech, 1200 E. California, Pasadena, CA 91125 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