High-frequency radio observations of the Kühr sample and the epoch-dependent luminosity function of flat-spectrum quasars

Abstract

We discuss our ATCA 18.5 and 22 GHz flux density measurements of Southern extragalactic sources in the complete 5 GHz sample of Kühr et al. (1981, A&AS, 45, 367). The high frequency (5-18.5 GHz) spectral indices of steep-spectrum sources for which we have 18.5 GHz data (66% of the complete sample) are systematically steeper than the low frequency (2.7-5 GHz) ones, with median α with luminosity. The completeness of 18.5 GHz data is much higher (89%) for flat-spectrum sources (mostly quasars), which also exhibit a spectral steepening: median α 5 2.7 = −0.14, median α 18.5 5 = 0.16 (S ν ∝ ν −α ), and median ∆α = 0.19. Taking advantage of the almost complete redshift information on flat-spectrum quasars, we have estimated their 5 GHz luminosity function in several redshift bins. The results confirm that their radio luminosity density peaks at z peak 2.5 but do not provide evidence for deviations from pure luminosity evolution as hinted at by other data sets. A comparison of our 22 GHz 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 5 GHz counts and luminosity functions of flat-spectrum radio quasars using the observed distribution of the 5-18.5 GHz 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.

High-frequency predictions for number counts and spectral properties of extragalactic radio sources. New evidence of a break at mm wavelengths in spectra of bright blazar sources

“…Ricci et al (2006) compared the 2.7-5 GHz and 5-18.5 GHz spectral indices and found a median steepening of Δα = 0.32.…”

THESPITZERVIEW OF FR I RADIO GALAXIES: ON THE ORIGIN OF THE NUCLEAR MID-INFRARED CONTINUUM

“…Considering that some absorption in the UV/optical bands is present, that the slope of the MIR spectrum agrees reasonably well with the synchrotron fit, and that no host corrections were applied the MIR emission in this source is likely to be mostly nonthermal. References: Morganti et al (1997) and Ricci et al (2006).…”

“…Interestingly, Pellegrini et al (2003) argue that the X-ray core in IC4296 (L 2−10 keV ∼ 1.6×10 41 erg s −1 intrinsic) originates from the jet and the X-rays are observed to be only mildly absorbed (N H ∼ 1×10 22 cm −2 ). References: Killeen et al (1986), Knapp et al (1989), Morganti et al (1997), Venturi et al (2000), Pellegrini et al (2003), and Ricci et al (2006).…”

The Deep X‐Ray Radio Blazar Survey. III. Radio Number Counts, Evolutionary Properties, and Luminosity Function of Blazars

“…The situation is only slightly better for FSRQs. Wall et al (2005) have recently studied the FSRQ LF and evolution using the Parkes 0.25 Jy sample, while Ricci et al (2006) had to use the Kühr et al (1981) 1 Jy sample to study the epoch dependency of the FSRQ LF. (The fact that Urry & Padovani [1995] used a 2 Jy sample for their review paper gives an idea of how slow progress in this field is.)…”