The local star formation rate and radio luminosity density

We present a new determination of the local volume-averaged star formation rate from the 1.4-GHz luminosity function of star forming galaxies. Our sample. taken from the B less than or equal to 12 Revised Shapley-Ames catalogue (231 normal spiral galaxies over an effective area of 7.1 sr) has 100 per cent complete radio detections and is insensitive to dust obscuration and cirrus contamination. After removal of known active galaxies. the best-fitting Schechter function has a faint-end slope of - 1.27 +/- 0.07 in agreement with the local Ha luminosity function. characteristic luminosity L-* = (2.6 +/- 0.7) x 10(22) W Hz(-1) and density phi(*) = (4.8 +/- 1.1) x 10(-4) Mpc(-3). The inferred local radio luminosity density of (1.73 +/- 0.37 +/- 0.03) x 10(19) W Hz(-1) Mpc(-3) (Poisson noise. large-scale structure fluctuations) implies a volume-averaged star formation rate similar to2 times larger than the Gallego et al. Halpha estimate, i.e. rho(1.4GHz) = (2.10 +/- 0.45 +/- 0.04) x 10(-2) M-. yr(-1) Mpc(-3) for a Salpeter initial mass function from 0.1-125 M-. and Hubble constant of 50 km s(-1) Mpc(-1).We demonstrate that the Balmer decrement is a highly unreliable extinction estimator, and argue that optical-ultraviolet (UV) star formation rates (SFRs) are easily underestimated, particularly at high redshift.