The Phoenix Deep Survey is a multi-wavelength survey based on deep 1.4 GHz radio imaging , reaching well into the sub-100 \mu Jy level .
One of the aims of this survey is to characterize the sub-mJy radio population , exploring its nature and evolution .
In this paper we present the catalog and results of the spectroscopic observations aimed at characterizing the optically “ bright ” ( R \lesssim 21.5 mag ) counterparts of faint radio sources .
Out of 371 sources with redshift determination , 21 % have absorption lines only , 11 % show AGN signatures , 32 % are star-forming galaxies , 34 % show narrow emission lines that do not allow detailed spectral classification ( due to poor signal-to-noise ratio and/or lack of diagnostic emission lines ) and the remaining 2 % are identified with stars .
For the star-forming galaxies with a Balmer decrement measurement we find a median extinction of A _ { H \alpha } = 1.9 mag , higher than that of optically selected samples .
This is a result of the radio selection , which is not biased against dusty systems .
Using the available spectroscopic information , we estimate the radio luminosity function of star-forming galaxies in two independent redshift bins at z \approx 0.1 and 0.3 respectively .
We find direct evidence for strong luminosity evolution of these systems consistent with L _ { 1.4 GHz } \propto ( 1 + z ) ^ { 2.7 } .