Journal Article

The radio luminosity function of radio-loud quasars from the 7C Redshift Survey

Chris J. Willott, Steve Rawlings, Katherine M. Blundell and Mark Lacy

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 300, issue 3, pages 625-648
Published in print November 1998 | ISSN: 0035-8711
Published online November 1998 | e-ISSN: 1365-2966 | DOI:
The radio luminosity function of radio-loud quasars from the 7C Redshift Survey

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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) radio flux density S151 > 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 (hereafter 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 7C and 3CRR samples, we have investigated the properties of RLQs as a function of redshift z and radio luminosity L151.

We derive the radio luminosity function (RLF) of RLQs and find that the data are well fitted by a single power law with slope α1 = 1.9 ± 0.1 (for H0 = 50 km s −1 Mpc−1, ΩM = 1, ΩΛ = 0). We find that there must be a break in the RLQ RLF at log10L151/W Hz−1 sr−1) ≲ 27, in order for the models to be consistent with the 7C and 6C source counts. The z-dependence of the RLF follows a one-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 redshifts.

A positive correlation between the radio and optical luminosities of 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 magnitudes of quasars in samples selected at low radio frequencies. We conclude that for samples with S151 ≲ 1 Jy, one must use optical data significantly deeper than the POSS-I limit (R ≈ 20), in order to avoid severe incompleteness.

Keywords: galaxies: active; galaxies: luminosity function, mass function; quasars: emission lines; quasars: general

Journal Article.  0 words. 

Subjects: Astronomy and Astrophysics

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