Tools for computing the AGN feedback: radio-loudness distribution and the kinetic luminosity function

TL;DR

This study analyzes the radio emission of over 1600 X-ray selected AGN to characterize their radio-loudness distribution and derive the kinetic luminosity function, revealing its dependence on luminosity and redshift.

Contribution

It provides the first nearly complete measurement of the radio/X-ray luminosity ratio distribution and derives the kinetic luminosity function for AGN, showing its evolution with redshift.

Findings

The probability distribution of radio/X-ray luminosity ratio spans 6 decades without bi-modality.

The likelihood of high radio/X-ray ratios increases at lower X-ray luminosities and possibly higher redshifts.

The kinetic energy density from AGN decreases by a factor of five below redshift 0.5.

Abstract

We studied the Active Galactic Nuclei (AGN) radio emission from a compilation of hard X-ray selected samples, all observed in the 1.4 GHz band. A total of more than 1600 AGN with 2-10 keV de-absorbed luminosities higher than 10^42 erg/s were used. For a sub-sample of about 50 z\lsim 0.1 AGN it was possible to reach a ~80% fraction of radio detections and therefore, for the first time, it was possible to almost completely measure the probability distribution function of the ratio between the radio and the X-ray luminosity Rx=log[L(1.4)/Lx]. The probability distribution function of Rx was functionally fitted as dependent on the X-ray luminosity and redshift, P(Rx|Lx,z). It roughly spans over 6 decades (-7<Rx<-1), and does not show any sign of bi-modality. It resulted that the probability of finding large values of the Rx ratio increases with decreasing X-ray luminosities and (possibly) with increasing redshift. No statistical significant difference was found between the radio properties of the X-ray absorbed and unabsorbed AGN. The measure of the probability distribution function of Rx allowed us to compute the kinetic luminosity function and the kinetic energy density which, at variance with what assumed in many galaxy evolution models, is observed to decrease of about a factor of five at redshift below 0.5. About half of the kinetic energy density results to be produced by the more radio quiet (Rx<-4) AGN. In agreement with previous estimates, the AGN efficiency in converting the accreted mass energy into kinetic power is, on average, ~5x10-3.