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 g alaxy. Since decimetric radiation does not suffer significant extinction an d is not directive, radio luminosities may thus provide a particularly stra ightforward way to determine the current rate of star formation. Using a sa mple of over 700 local galaxies, we confirm the utility of the radio lumino sity as a measure of star formation rate by showing concordance with the ra tes predicted by U-band, H alpha, and far-infrared luminosities. We also sh ow that there are systematic discrepancies between these various indicators , suggesting that the H alpha luminosity may underestimate the star formati on rate by approximately an order of magnitude when the star formation rate is greater than or similar to 20 M. yr(-1). We use this calibration and th e measured radio luminosities of sub-may radio sources to infer the star fo rmation rate in approximately 60 star-forming galaxies at moderate (z great er than or similar to 0.1) redshifts, both as the actual rate and as the fr action of the existing mass of stars in the galaxy. For some of these objec ts, the inferred current rate of star formation could increase the stellar mass in the galaxy by approximately 10% over an interval of approximate to 30 Myr.