Calibrating Star Formation in WISE using Total Infrared Luminosity

We present accurate resolved $WISE$ photometry of galaxies in the combined SINGS and KINGFISH sample. The luminosities in the W3 12$\mu$m and W4 23$\mu$m bands are calibrated to star formation rates (SFRs) derived using the total infrared luminosity, avoiding UV/optical uncertainties due to dust extinction corrections. The W3 relation has a 1-$\sigma$ scatter of 0.15 dex over nearly 5 orders of magnitude in SFR and 12$\mu$m luminosity, and a range in host stellar mass from dwarf (10$^7$ M$_\odot$) to $\sim3\times$M$_\star$ (10$^{11.5}$ M$_\odot$) galaxies. In the absence of deep silicate absorption features and powerful active galactic nuclei, we expect this to be a reliable SFR indicator chiefly due to the broad nature of the W3 band. By contrast the W4 SFR relation shows more scatter (1-$\sigma =$ 0.18 dex). Both relations show reasonable agreement with radio continuum-derived SFRs and excellent accordance with so-called "hybrid" H$\alpha + 24 \mu$m and FUV$+$24$\mu$m indicators. Moreover, the $WISE$ SFR relations appear to be insensitive to the metallicity range in the sample. We also compare our results with IRAS-selected luminous infrared galaxies, showing that the $WISE$ relations maintain concordance, but systematically deviate for the most extreme galaxies. Given the all-sky coverage of $WISE$ and the performance of the W3 band as a SFR indicator, the $L_{12\mu \rm m}$ SFR relation could be of great use to studies of nearby galaxies and forthcoming large area surveys at optical and radio wavelengths.