Reference Spectra in the “Artificial-Moon” Scale and Cosmological Studies of Radio Sources

Abstract

We present the modified version of the flux scale [1] of cosmic radio sources. The number of standard sources is increased, the dynamical range of the scale is extended by one order of magnitude toward weak fluxes, and the standard sources are distributed more uniformly over the northern hemisphere. The scale [1] at frequencies above 15 GHz is improved with allowance for additional data. New standard sources are determined in the millimeter wavelength range. The spectra of standard sources are obtained on the basis of accurate absolute measurements of the radiation flux density at frequencies 0.5-10 GHz by the method of an “artificial moon.” Spectrum shapes of the standard sources were determined by the method of relative spectra based on relative measurements in the frequency interval from 26 MHz to 31.4 GHz. This makes it possible to find spectra in the entire frequency range with an accuracy of 3-4%. We determined the spectra of more than 100 steep-spectrum extra-Galactic sources in the “artificial-moon'' scale. Most spectra have breaks in the frequency interval from 178 MHz to 14.9 GHz. The spectra of some sources have constant spectral indices. The distributions of the break frequencies of radio galaxies and quasars over celestial coordinates of these sources are obtained. These distributions are close to lognormal. The frequencies of the maxima of radio-galaxy and quasar distributions are equal to 1.25 and 2.5 GHz, respectively. The mean spectral indices as functions of frequency are determined for radio galaxies and quasars. The spectral indices of sources belonging to these two groups increase with frequency at the same rate below 3 GHz. At higher frequencies, the slope of the mean spectrum of galaxies remains the same, while the mean quasar spectrum flattens.