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We present results from a decimetric radio survey undertaken with the Very Large Array (VLA) 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 1.4 GHz luminosities are compared with earlier nebular emission line and ultraviolet (UV) continuum diagnostics. We find broad correlations, over several decades in luminosity, between Hα, the UV continuum and 1.4 GHz 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.

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, H-alpha, and far-infrared luminosites. We also show that there are systematic discrepancies between these various indicators, suggesting that the H-alpha luminosity may underestimate the star formation rate by approximately an order of magnitude when the star formation rate is more than 20 solar mass per year. 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 about 30 Myr.Comment: 15 pages, 3 diagram

The initial Phoenix Deep Survey (PDS) observations with the Australia Telescope Compact Array have been supplemented by additional 1.4 GHz observations over the past few years. Here we present details of the construction of a new mosaic image covering an area of 4.56 square degrees, an investigation of the reliability of the source measurements, and the 1.4 GHz source counts for the compiled radio catalogue. The mosaic achieves a 1σ rms noise of 12 µJy at its most sensitive, and a homogeneous radio-selected catalogue of over 2000 sources reaching flux densities as faint as 60 µJy has been compiled. The source parameter measurements are found to be consistent with the expected uncertainties from the image noise levels and the Gaussian source fitting procedure. A radio-selected sample avoids the complications of obscuration associated with optically-selected samples, and by utilising complementary PDS observations including multicolour optical, near-infrared and spectroscopic data, this radio catalogue will be used in a detailed investigation of the evolution in star-formation spanning the redshift range 0 < z < 1. The homogeneity of the catalogue ensures a consistent picture of galaxy evolution can be developed over the full cosmologically significant redshift range of interest. The 1.4 GHz mosaic image and the source catalogue are available on the web at http://www.atnf.csiro.au/~ahopkins/phoenix/ or from the authors by request.

We present the first results from the Phoenix Deep Survey, a multiwavelength survey of a 2° diameter region. Observations in the radio continuum at 1.4 GHz carried out with the Australia Telescope Compact Array are described. The catalogue of over 1000 radio sources compiled from these observations is analysed, and the source counts are presented. We model the observational source counts using a two‐population model and published luminosity functions for these populations. Upon invoking luminosity and density evolution, we find that a luminosity evolution model best fits the radio observations, consistent with earlier work. The redshift distribution of the two galaxy populations investigated is also modelled and discussed.