2012ApJ...760....6M

Using data from the mid-infrared to millimeter wavelengths for individual galaxies and for stacked ensembles at 0.5 < z < 2, we derive robust estimates of dust masses (M_dust) for main-sequence (MS) galaxies, which obey a tight correlation between star formation rate (SFR) and stellar mass (M_*), and for starbursting galaxies that fall outside that relation. Exploiting the correlation of gas-to-dust mass with metallicity (M_gas/M_dust-Z), we use our measurements to constrain the gas content, CO-to-H₂conversion factors (α_CO), and star formation efficiencies (SFE) of these distant galaxies. Using large statistical samples, we confirm that α_COand SFE are an order of magnitude higher and lower, respectively, in MS galaxies at high redshifts compared to the values of local galaxies with equivalently high infrared luminosities (L_IR> 10¹² L_☉). For galaxies within the MS, we show that the variations of specific star formation rates (sSFRs = SFR/M_*) are driven by varying gas fractions. For relatively massive galaxies like those in our samples, we show that the hardness of the radiation field, < U > , which is proportional to the dust-mass-weighted luminosity (L_IR/M_dust) and the primary parameter defining the shape of the IR spectral energy distribution (SED), is equivalent to SFE/Z. For MS galaxies with stellar mass log (M_*/M_☉) ≥ 9.7 we measure this quantity, < U > , showing that it does not depend significantly on either the stellar mass or the sSFR. This is explained as a simple consequence of the existing correlations between SFR-M_*, M_*-Z, and M_gas-SFR. Instead, we show that < U > (or equally L_IR/M_dust) does evolve, with MS galaxies having harder radiation fields and thus warmer temperatures as redshift increases from z = 0 to 2, a trend that can also be understood based on the redshift evolution of the M_*-Z and SFR-M_*relations. These results motivate the construction of a universal set of SED templates for MS galaxies that are independent of their sSFR or M_* but vary as a function of redshift with only one parameter, < U > .