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

摘要

We present models to predict high frequency counts of extragalactic radiosources using physically grounded recipes to describe the complex spectralbehaviour of blazars, that dominate the mm-wave counts at bright fluxdensities. We show that simple power-law spectra are ruled out byhigh-frequency (nu>100 GHz) data. These data also strongly constrain modelsfeaturing the spectral breaks predicted by classical physical models for thesynchrotron emission produced in jets of blazars (Blandford & Konigl 1979;Konigl 1981). A model dealing with blazars as a single population is, at best,only marginally consistent with data coming from current surveys at high radiofrequencies. Our most successful model assumes different distributions of breakfrequencies, nu_M, for BL Lacs and Flat-Spectrum Radio Quasars (FSRQs). Theformer objects have substantially higher values of nu_M, implying that thesynchrotron emission comes from more compact regions; therefore, a substantialincrease of the BL Lac fraction at high radio frequencies and at bright fluxdensities is predicted. Remarkably, our best model is able to give a very goodfit to all the observed data on number counts and on distributions of spectralindices of extragalactic radio sources at frequencies above 5 and up to 220GHz. Predictions for the forthcoming sub-mm blazar counts from Planck, at thehighest HFI frequencies, and from Herschel surveys are also presented.