Astronomy and Astrophysics, volume 445, 465-469 (2006/1-2)
High-frequency radio observations of the Kuehr sample and the epoch-dependent luminosity function of flat-spectrum quasars.
RICCI R., PRANDONI I., GRUPPIONI C., SAULT R.J. and DE ZOTTI G.
Abstract (from CDS):
We discuss our ATCA 18.5 and 22GHz flux density measurements of Southern extragalactic sources in the complete 5GHz sample of Kuehr et al. (1981A&AS...45..367K
). The high frequency (5-18.5GHz) spectral indices of steep-spectrum sources for which we have 18.5GHz data (66% of the complete sample) are systematically steeper than the low frequency (2.7-5GHz) ones, with median α52.7
=0.76, median α18.55
), and median steepening Δα=0.32, and there is evidence of an anti-correlation of Δα18.55
with luminosity. The completeness of 18.5GHz data is much higher (89%) for flat-spectrum sources (mostly quasars), which also exhibit a spectral steepening: median α52.7
=-0.14, median α18.55
), and median Δα=0.19. Taking advantage of the almost complete redshift information on flat-spectrum quasars, we have estimated their 5GHz luminosity function in several redshift bins. The results confirm that their radio luminosity density peaks at zpeak
≃2.5 but do not provide evidence for deviations from pure luminosity evolution as hinted at by other data sets. A comparison of our 22GHz flux densities with WMAP K-band data for flat-spectrum sources suggests that WMAP flux densities may be low by a median factor of ≃1.2. The extrapolations of 5GHz counts and luminosity functions of flat-spectrum radio quasars using the observed distribution of the 5-18.5GHz spectral indices match those derived directly from WMAP data, indicating that the high frequency WMAP survey does not detect any large population of FSRQs with anomalous spectra.
radio continuum: general - galaxies: nuclei - quasars: general - galaxies: luminosity function, mass function
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<Available at CDS (J/A+A/445/465): table1.dat>
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