On the Evolution of the Cores of Radio Sources and Their Extended Radio Emission

TL;DR

This study investigates the evolution of radio-loud AGN cores and their extended emission, revealing that cores decline in number density with redshift and do not co-evolve with extended lobes, based on radio luminosity functions.

Contribution

It provides the first detailed analysis of the separate evolution of AGN cores and extended lobes using large radio samples and luminosity functions.

Findings

Core RLF declines with redshift, indicating negative density evolution.

Core and total RLFs differ significantly, suggesting different evolutionary paths.

Cores and extended lobes do not co-evolve at radio emission.

Abstract

The work in this paper aims at determining the evolution and possible co-evolution of radio-loud active galactic nuclei (AGNs) and their cores via their radio luminosity functions (i.e., total and core RLF respectively). Using a large combined sample of 1063 radio-loud AGNs selected at low radio frequency, we investigate the radio luminosity function (RLF) at 408 MHz of steep-spectrum radio sources. Our results support a luminosity-dependent evolution. Using core flux density data of the complete sample 3CRR, we investigate the core RLF at 5.0 GHz. Based on the combined sample with incomplete core flux data, we also estimate the core RLF using a modified factor of completeness. Both results are consistent and show that the comoving number density of radio cores displays a persistent decline with redshift, implying a negative density evolution. We find that the core RLF is obviously different from the total RLF at 408 MHz band which is mainly contributed by extended lobes, implying that the cores and extended lobes could not be co-evolving at radio emission.