Star formation rates in faint radio galaxies

The decimetric radio continuum luminosity of a star-forming galaxy appears to be directly proportional to the rate of formation of supernovae in the galaxy. Since decimetric radiation does not suffer significant extinction and is not directive, radio luminosities may thus provide a particularly straightforward way to determine the current rate of star formation. Using a sample of over 700 local galaxies, we confirm the utility of the radio luminosity as a measure of star formation rate by showing concordance with the rates predicted by U-band, Hα, and far-infrared luminosities. We also show that there are systematic discrepancies between these various indicators, suggesting that the Hα luminosity may underestimate the star formation rate by approximately an order of magnitude when the star formation rate is ≳20 M_⊙ yr^-1. We use this calibration and the measured radio luminosities of sub-mJy radio sources to infer the star formation rate in approximately 60 star-forming galaxies at moderate (z ≳ 0.1) redshifts, both as the actual rate and as the fraction of the existing mass of stars in the galaxy. For some of these objects, the inferred current rate of star formation could increase the stellar mass in the galaxy by approximately 10% over an interval of ≈ 30 Myr.