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  Astrophysics


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

Authors: R. Ricci </find/astro-ph/1/au:+Ricci_R/0/1/0/all/0/1> (1,2), I.
Prandoni </find/astro-ph/1/au:+Prandoni_I/0/1/0/all/0/1> (3), G.
Gruppioni </find/astro-ph/1/au:+Gruppioni_G/0/1/0/all/0/1> (4), R.J.
Sault </find/astro-ph/1/au:+Sault_R/0/1/0/all/0/1> (2), G. De Zotti
</find/astro-ph/1/au:+Zotti_G/0/1/0/all/0/1> (5,1) ((1) Sissa/Isas, (2)
Atnf, (3) Inaf-Ira, (4) Inaf-Bologna, (5) Inaf-Padua)
(Submitted on 20 Sep 2005)

    Abstract: We discuss our ATCA 18.5 and 22 GHz flux density
    measurements of the Southern extragalactic sources in the complete
    5-GHz sample of Kuehr et al. (1981). 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, and there is
    evidence of an anti-correlation of high-frequency spectral index
    with luminosity. The completeness of the 18.5-GHz data is much
    higher (89%) for flat-spectrum sources (mostly quasars), which also
    exhibit a spectral steepening. 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 \simeq 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 density with WMAP K-band data for
    flat-spectrum sources suggests that WMAP flux densities may be low
    by a median factor of \simeq 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. 

Comments: 	11 pages, 5 figures, 1 table, accepted on A&A
Subjects: 	Astrophysics (astro-ph)
Cite as: 	arXiv:astro-ph/0509580v1 </abs/astro-ph/0509580v1>