  Using a deep Australia Telescope Compact Array (ATCA) radio survey covering
an area of ~3deg^{2} to a 4\sigma sensitivity of \ge 100 \muJy at 1.4GHz, we
study the nature of faint radio galaxies. About 50% of the detected radio
sources are identified with an optical counterpart revealed by CCD photometry
to m_{R}=22.5 mag. Near-infrared (K-band) data are also available for a
selected sample of the radio sources, while spectroscopic observations have
been carried out for about 40% of the optically identified sample. These
provide redshifts and information on the stellar content. Emission-line ratios
imply that most of the emission line sources are star-forming galaxies, with a
small contribution (\approx 10%) from Sy1/Sy2 type objects. We also find a
significant number of absorption line systems, likely to be ellipticals. These
dominate at high flux densities (> 1 mJy) but are also found at sub-mJy levels.
Using the Balmer decrement we find a visual extinction A_{V}=1.0 for the
star-forming faint radio sources. This moderate reddening is consistent with
the V-R and R-K colours of the optically identified sources. For emission line
galaxies, there is a correlation between the radio power and the H\alpha
luminosity, in agreement with the result of Benn et al. (1993). This suggests
that the radio emission of starburst radio galaxies is a good indicator of
star-formation activity.
