Massive Lyman Break Galaxies at z ~ 3 in the Spitzer Extragalactic First Look Survey

Abstract

We investigate the properties of 1088 Lyman break galaxies (LBGs) at z ~ 3 selected from a ~2.63 deg^2 subregion of the First Look Survey field using the ground-based multicolor data and the Spitzer Space Telescope mid-infrared data at 3-8 and 24 μm. With the wide area and the broad wavelength coverage, we sample a large number of "rare" u-band dropouts that are massive (M_* > 10^(11) M_☉), allowing us to perform a statistical analysis of these subsets of LBGs which have not been studied in detail. Optically bright (R_(AB) ≤ 24.5 mag) LBGs detected in mid-infrared (S_(3.6 μm) ≥ 6 μJy) reside at the most massive and dusty end of the LBG population, with relatively high and tight M/L in rest-frame near-infrared. Most infrared-luminous LBGs (S_(24 μm) ≥ 100 μJy) are dusty star-forming galaxies with star formation rates of 100-1000 M_☉ yr^(-1), total infrared luminosity of >10^(12) L_☉. By constructing the UV luminosity function of massive LBGs, we estimate that the lower limit for the star formation rate density from LBGs more massive than 10^(11) M_☉ at z ~ 3 is ≥ 3.3 × 10^(-3) M_☉^(-1) yr^(-1) Mpc^(-3), showing for the first time that the UV-bright population of massive galaxies alone contributes significantly to the global star formation rate density at z ~ 3. When combined with the star formation rate densities at z < 2, our result reveals a steady increase in the contribution of massive galaxies to the global star formation from z = 0 to z ~ 3, providing strong support to the downsizing of galaxy formation.

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