Star formation rates of star-forming galaxies from the WISE all-sky survey

We explore correlations between extinction-corrected Hα, Hβ and [O II]_double luminosities versus 12- and 22-μm band luminosities, based on matching samples from the Sloan Digital Sky Survey (SDSS) and the Wide-field Infrared Survey Explorer (WISE). All the coefficients show strong correlations between Balmer lines and mid-infrared (MIR) luminosities, while the extinction-corrected [O II]_double shows a weaker correlation with MIR luminosities. The extinction-corrected emission-line (EL) luminosities are more tightly correlated with linear combinations of EL(obs) and MIR luminosities than with pure MIR luminosities. Linear combinations include both direct and dust-obscured star formation activity in galaxies and offer an improved star formation rate (SFR) indicator for star-forming galaxies. The factor that causes log₁₀L_MIR/log₁₀L_Hα to vary is the metallicity. We find that log₁₀(L_Hα(obs) + α × L_MIR) and log₁₀(L[O II]_double(obs) + α × L_MIR), rather than pure MIR luminosities or L[O II]_double alone, are good proxies for extinction-corrected log₁₀L_Hα, with a residual that is independent of metallicity. The morphologies have weak correlations with log₁₀L_MIR/log₁₀L_EL ratios. E(B - V) can be estimated by log₁₀[L_MIR/L_Hα(obs)].