The nature of the faint radio source population and star formation history derived from sub-MJY surveys

We present new results on the nature of the faint radio galaxy population obtained from a deep identification study in the Marano Field. This work represents the highest identification fractions attained to date in literature for sub-mJy radio samples. Star-forming galaxies constitute a significant fraction of the optical counterparts of sub-mJy radio sources, although they are not the dominant identification class (as formerly believed). We also present a new determination of the co-moving star formation density from z = 0 to z similar or equal to 0.35 using the radio luminosity function of star-forming galaxies. For the local determination, we used a sample of 231 spiral galaxies taken from the B less than or equal to 12 Revised Shapley-Ames Catalogue, while for the non-local determination, we used a sample of 87 star-forming galaxies taken from the Benn et al. (1993) sample. The inferred local star formation rate is about twice as great as the H-alpha estimate, while the intermediate 0.05 < z < 0.35 star formation rate is consistent with coeval ultraviolet and H-alpha estimates. This is due to large-scale structure, rarely accounted for in estimates of the cosmic star formation history; the situation could improve significantly with deep moderate-area radio surveys.