THE RADIO LUMINOSITY FUNCTION OF RADIO-LOUD QUASARS FROM THE 7C REDSHIFT SURVEY

We present a complete sample of 24 radio-loud quasars (RLQs) from the new 7C Redshift Survey. Every quasar with a low-frequency (151 MHz) ra dio flux density Si-151 > 0.5 JY in two regions of the sky covering 0. 013 sr is included; 23 of these have sufficient extended flux to meet the selection criteria, 18 of these have steep radio spectra (hereafte r denoted as SSQs). The key advantage of this sample over most samples of RLQs is the lack of an optical magnitude limit. By combining the 7 C and 3CRR samples? we have investigated the properties of RLQs as a f unction of redshift z and radio luminosity L-151. We derive the radio luminosity function (RLF) of RLQs and find that the data are well fitt ed by a single power law with slope alpha(1) = 1.9 +/- 0.1 (for H-0 = 50 km s(-1) Mpc(-1), Omega(M) = 1, Omega(Lambda) = 0). We find that th ere must be a break in the RLQ RLF at log10(L-151/W Hz(-1) sr(-1)) les s than or similar to 27, in order for the models to be consistent with the 7C and 6C source counts. The z-dependence of the RLF follows a on e-tailed Gaussian which peaks at z = 1.7 +/- 0.2. We find no evidence for a decline in the comoving space density of RLQs at higher redshift s. A positive correlation between the radio and optical luminosities o f SSQs is observed, confirming a result of Serjeant et al. We are able to rule out this correlation being the result of selection effects or biases in our combined sample. The radio-optical correlation and best fitting model RLF enable us to estimate the distribution of optical m agnitudes of quasars in samples selected at low radio frequencies. We conclude that for samples with S-151 less than or similar to 1 Jy, one must use optical data significantly deeper than the POSS-I Limit (R a pproximate to 20), in order to avoid severe incompleteness.