  We present results from a decimetric radio survey undertaken with the Very
Large Array as part of a longer term goal to inter-compare star formation and
dust extinction diagnostics, on a galaxy by galaxy basis, for a representative
sample of nearby galaxies. For our survey field, Selected Area 57, star
formation rates derived from 1.4GHz luminosities are compared with earlier
nebular emission line and ultraviolet (UV) continuum diagnostics. We find broad
correlations, over several decades in luminosity, between H-alpha, the UV
continuum and 1.4GHz diagnostics. However, the scatter in these relations is
found to be larger than observational errors, with offsets between the observed
relations and those expected assuming constant star-formation histories and
luminosity-independent extinction models. We investigate the physical origin of
the observed relations, and conclude the discrepancies between different
star-formation diagnostics can only be partly explained by simple models of
dust extinction in galaxies. These models cannot by themselves explain all the
observed differences, introducing the need for temporally varying
star-formation histories and/or more complex models of extinction, to explain
the entire dataset.
