Volume 533, September 2011
|Number of page(s)||21|
|Published online||29 August 2011|
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⋆
LAL, Univ Paris-Sud, CNRS/IN2P3, Orsay, France
2 Departamento de Física, Universidad de Oviedo, c. Calvo Sotelo s/n, 33007 Oviedo, Spain
3 Research Unit associated with IFCA-CSIC, Instituto de Física de Cantabria, avda. los Castros, s/n, 39005 Santander, Spain
4 INAF – Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
5 International School for Advanced Studies, SISSA/ISAS, Astrophysics Sector, via Bonomea 265, 34136 Trieste, Italy
6 Instituto de Física de Cantabria, CSIC-Universidad de Cantabria, Avda. de los Castros s/n, 39005 Santander, Spain
Received: 28 March 2011
Accepted: 9 June 2011
We present models to predict high-frequency counts of extragalactic radio sources using physically grounded recipes to describe the complex spectral behaviour of blazars that dominate the mm-wave counts at bright flux densities. We show that simple power-law spectra are ruled out by high-frequency (ν ≥ 100 GHz) data. These data also strongly constrain models featuring the spectral breaks predicted by classical physical models for the synchrotron emission produced in jets of blazars. A model dealing with blazars as a single population is, at best, only marginally consistent with data coming from current surveys at high radio frequencies. Our most successful model assumes different distributions of break frequencies, νM, for BL Lacs and flat-spectrum radio quasars (FSRQs). The former objects have substantially higher values of νM, implying that the synchrotron emission comes from more compact regions; therefore, a substantial increase of the BL Lac fraction at high radio frequencies and at bright flux densities is predicted. Remarkably, our best model is able to give a very good fit to all the observed data on number counts and on distributions of spectral indices of extragalactic radio sources at frequencies above 5 and up to 220 GHz. Predictions for the forthcoming sub-mm blazar counts from Planck, at the highest HFI frequencies, and from Herschel surveys are also presented.
Key words: galaxies: active / galaxies: statistics / radio continuum: galaxies / catalogs
Appendices are available in electronic form at http://www.aanda.org
© ESO, 2011
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