Massive Lyman break galaxies at z ∼ 3 in the Spitzer extragalactic first look survey

We investigate the properties of 1088 Lyman break galaxies (LBGs) at z ∼ 3 selected from a ∼2.63 deg² 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* > 10¹¹ 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 MIL 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 >10¹²L_⊙. 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 10¹¹ 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.