Mean and Extreme Radio Properties of Quasars and the Origin of Radio Emission

TL;DR

This study examines how quasars' radio properties evolve with various parameters, revealing that radio-loudness and radio luminosity increase with black hole mass and decrease in accretion rate, with implications for quasar classification.

Contribution

It provides new insights into the evolution of radio-loud fractions and mean radio-loudness of quasars as functions of redshift, luminosity, black hole mass, and wind properties.

Findings

Radio-loud fraction and mean radio luminosity increase with black hole mass.

Both metrics increase with decreasing accretion rate.

Radio-loud and radio-quiet quasars may be parallel sequences.

Abstract

We investigate the evolution of both the radio-loud fraction (RLF) and (using stacking analysis) the mean radio-loudness of quasars. We consider how these values evolve as a function of redshift and luminosity, black hole (BH) mass and accretion rate, and parameters related to the dominance of a wind in the broad emission line region. We match the FIRST source catalog to samples of luminous quasars (both spectroscopic and photometric), primarily from the Sloan Digital Sky Survey. After accounting for catastrophic errors in BH mass estimates at high-redshift, we find that both the RLF and the mean radio luminosity increase for increasing BH mass and decreasing accretion rate. Similarly both the RLF and mean radio loudness increase for quasars which are argued to have weaker radiation line driven wind components of the broad emission line region. In agreement with past work, we find that the RLF increases with increasing luminosity and decreasing redshift while the mean radio-loudness evolves in the exact opposite manner. This difference in behavior between the mean radio-loudness and the RLF in L-z may indicate selection effects that bias our understanding of the evolution of the RLF; deeper surveys in the optical and radio are needed to resolve this discrepancy. Finally, we argue that radio-loud (RL) and radio-quiet (RQ) quasars may be parallel sequences but where only RQ quasars at one extreme of the distribution are likely to become RL, possibly through slight differences in spin and/or merger history.