SIMBAD references

We present spectra for a sample of radio sources from the FIRST survey, and use them to define the form of the redshift distribution of radio sources at mJy levels. We targeted 365 sources and obtained 46 redshifts (13per cent of the sample). We find that our sample is complete in redshift measurement to R∼18.6, corresponding to z∼0.2. Galaxies were assigned spectral types based on emission-line strengths. Early-type galaxies represent the largest subset (45per cent) of the sample and have redshifts 0.15≲z≲0.5; late-type galaxies make up 15per cent of the sample and have redshifts 0.05≲z≲0.2; starbursting galaxies are a small fraction (∼6per cent), and are very nearby (z≲0.05). Some 9per cent of the population have Seyfert 1/quasar-type spectra, all at z≳0.8, and 4per cent are Seyfert 2 type galaxies at intermediate redshifts (z∼0.2).

Using our measurements and data from the Phoenix survey (Hopkins et al.), we obtain an estimate for N(z) at S_1.4GHz≥1mJy and compare this with model predictions. At variance with previous conclusions, we find that the population of starbursting objects makes up ≲5per cent of the radio population at S∼1mJy.