2010ApJ...723..129K

We study the evolution of star formation activity of galaxies at 0.5 < z < 3.5 as a function of stellar mass, using very deep NIR data taken with the Multi-Object Infrared Camera and Spectrograph on the Subaru telescope in the GOODS-North region. The NIR imaging data reach K∼ 23-24 Vega magnitude and they allow us to construct a nearly stellar-mass-limited sample down to ∼10^9.5–10 M_☉ even at z ∼ 3. We estimated star formation rates (SFRs) of the sample with two indicators, namely, the Spitzer/MIPS 24 µm flux and the rest-frame 2800 Å luminosity. The SFR distribution at a fixed M_star shifts to higher values with increasing redshift at 0.5 < z < 3.5. More massive galaxies show stronger evolution of SFR at z >< 1. We found galaxies at 2.5 < z < 3.5 show a bimodality in their SSFR distribution, which can be divided into two populations by a constant SSFR of ∼2/Gyr. Galaxies in the low-SSFR group have SSFRs of ∼0.5-1.0/Gyr, while the high-SSFR population shows ∼10/Gyr. The cosmic SFR density (SFRD) is dominated by galaxies with M_star= 10^10–11 M_☉ at 0.5 < z < 3.5, while the contribution of massive galaxies with M_star= 10^11–11.5 M_☉shows a strong evolution at z>1 and becomes significant at z ∼ 3, especially in the case with the SFR based on MIPS 24 µm. In galaxies with M_star= 10^10–11.5 M_☉, those with a relatively narrow range of SSFR (<1 dex) dominates the cosmic SFRD at 0.5 < z < 3.5. The SSFR of galaxies that dominate the SFRD systematically increases with redshift. At 2.5 < z < 3.5, the high-SSFR population, which is relatively small in number, dominates the SFRD. Major star formation in the universe at higher redshift seems to be associated with a more rapid growth of stellar mass of galaxies.