A mixture evolution scenario of the AGN radio luminosity function. II. Do low- and high-power radio-loud AGNs evolve differently?

TL;DR

This study confirms that the cosmic evolution of steep-spectrum radio-loud AGNs can be explained by a combined density and luminosity evolution model, which accounts for luminosity-dependent evolution and suggests similar evolution for low- and high-power AGNs.

Contribution

It introduces a mixture evolution scenario that successfully models the evolution of radio-loud AGNs and shows no need for different evolution paths based on power.

Findings

Density evolution increases slowly then decreases rapidly with redshift.

Luminosity evolution rapidly increases up to high redshift.

No significant difference in evolution between low- and high-power radio-loud AGNs.

Abstract

Following previous work, we further confirm that the cosmic evolution of steep-spectrum radio-loud AGNs (active galactic nuclei) can be reproduced by a simple combination of density evolution (DE) and luminosity evolution (LE). This mixture evolution scenario can naturally explain the luminosity-dependent evolution of radio-loud AGNs. Our models successfully fitted a large amount of data on radio luminosity functions (RLFs) of steep-spectrum sources and multi-frequency source counts. The modeling indicates that the DE slowly increase as $(1+z)^{0.3 \thicksim 1.3}$ out to $z \thicksim 0.8$, and then rapidly decreases as $(1+z)^{-6.8 \thicksim -5.7}$, while the LE rapidly increase as $(1+z)^{4.8}$ out to a higher redshift (at least $z>3.5$). We find a high-redshift decline (i.e. redshift cutoff) in the number density of steep-spectrum radio sources, but we cannot conclude whether such decline is sharp or shallow. We believe that whether a redshift cutoff occurs or not depends mainly on DE, while its steepness is decided by LE, which, however, cannot be well constrained due to the lack of high-redshift samples. Most intriguingly, according to our mixture evolution scenario, there appears to be no need for different evolution for the low- and high-power radio-loud AGNs. Both types of sources experience the same combined evolution of DE and LE.