2014MNRAS.438...97W

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 log10LMIR/log10LHα to vary is the metallicity. We find that log10(LHα(obs) + αxLMIR) and log_10(L[O II]_double(obs)+α×L_MIR), rather than pure MIR luminosities or [O II]_double alone, are good proxies for extinction-corrected log10LHα, with a residual that is independent of metallicity. The morphologies have weak correlations with log10LMIR/log10LEL ratios. E(B - V) can be estimated by log10[LMIR/LHα(obs)].