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 similar to 3 selected from a similar to 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 mu m. 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-circle dot), 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 mu m >= 6 mu Jy) 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 (mu m) >= 100 mu Jy) are dusty star-forming galaxies with star formation rates of 100-1000 M-circle dot yr(-1), total infrared luminosity of > 10(12) L-circle dot. 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-circle dot at z similar to 3 is >= 3.3; 10(-3) M-circle dot(-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 similar to 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 similar to 3, providing strong support to the downsizing of galaxy formation.