Estimating Star Formation Rates from Infrared and Radio Luminosities: The Origin of the Radio‐Infrared Correlation

I have assembled a diverse sample of galaxies from the literature with far-ultraviolet (FUV), optical, infrared (IR) and radio luminosities to explore the calibration of radio-derived and IR-derived star formation (SF) rates, and the origin of the radio-IR correlation. By comparing the 8-1000 micron IR, which samples dust-reprocessed starlight, with direct stellar FUV emission, I show that the IR traces most of the SF in luminous L* galaxies but traces only a small fraction of the SF in faint ~0.01 L* galaxies. If radio emission were a perfect SF rate indicator, this effect would cause easily detectable curvature in the radio-IR correlation. Yet, the radio-IR correlation is nearly linear. This implies that the…