On the evolution and environmental dependence of the star formation rate versus stellar mass relation since z ∼ 2

This paper discusses the evolution of the correlation between galaxy star formation rates (SFRs) and stellar mass (M-*) over the last similar to 10 Gyr, particularly focusing on its environmental dependence. We first present the mid-infrared (MIR) properties of the H alpha-selected galaxies in a rich cluster Cl 0939+4713 at z = 0.4. We use wide-field Spitzer/MIPS 24 mu m data to show that the optically red H alpha emitters, which are most prevalent in group-scale environments, tend to have higher SFRs and higher dust extinction than the majority population of blue H alpha sources. With an MIR stacking analysis, we find that the median SFR of H alpha emitters is higher in higher density environment at z = 0.4. We also find that star-forming galaxies in high-density environment tend to have higher specific SFR (SSFR), although the trend is much less significant compared to that of SFR. This increase of SSFR in high-density environment is not visible when we consider the SFR derived from H alpha alone, suggesting that the dust attenuation in galaxies depends on environment; galaxies in high-density environment tend to be dustier (by up to similar to 0.5 mag), probably reflecting a higher fraction of nucleated, dusty starbursts in higher density environments at z = 0.4. We then discuss the environmental dependence of the SFR-M-* relation for star-forming galaxies since z similar to 2, by compiling our comparable, narrow-band-selected, large H alpha emitter samples in both distant cluster environments and field environments. We find that the SSFR of H alpha-selected galaxies (at the fixed mass of log (M-*/M-circle dot) = 10) rapidly evolves as (1 + z)(3), but the SFR-M-* relation is independent of the environment since z similar to 2, as far as we rely on the H alpha-based SFRs (with M-*-dependent extinction correction). Even if we consider the possible environmental variation in the dust attenuation, we conclude that the difference in the SFR-M-* relation between cluster and field star-forming galaxies is always small (less than or similar to 0.2 dex level) at any time in the history of the Universe since z similar to 2.