A new sample of large angular size radio galaxies. III. Statistics and evolution of the grown population

TL;DR

This study analyzes a new sample of large angular size FR I and FR II radio galaxies, comparing their properties, evolution, and environmental influences, and finds no evidence for FR II to FR I evolution or size-dependent core power differences.

Contribution

It provides a detailed statistical analysis of large radio galaxies, highlighting differences between FR I and FR II classes and their evolution in low-density environments.

Findings

FR I and FR II distinctions correlate with radio power.

Asymmetries are mainly due to environmental anisotropies.

Giant radio galaxies are likely older, evolved FR I/II objects.

Abstract

We present in this paper a detailed study of a new sample of large angular size FR I and FR II radio galaxies and compare the properties of the two classes. As expected, a pure morphology based distinction of FR Is and FR IIs corresponds to a break in total radio power. The radio cores in FR Is are also weaker than in FR IIs, although there is not a well defined break power. We find that asymmetry in the structure of the sample members must be the consequence of anisotropies in the medium where the lobes expand, with orientation playing a minor role. Moreover, literature data and our observations at kiloparsec scales suggest that the large differences between the structures of FR I and FR II radio galaxies must arise from the poorly known central kiloparsec region of their host galaxies. We analyze the sub-sample of giant radio galaxies, and do not find evidence that these large objects require higher core powers. Our results are consistent with giant radio galaxies being the older population of normal FR I and FR II objects evolving in low density environments. Comparing results from our sample with predictions from the radio luminosity function we find no evidence of a possible FR II to FR I evolution. Moreover, we conclude that at z~0.1, one out of four FR II radio sources has a linear size above 500 kpc, thus being in an advanced stage of evolution (for example, older than ~10 Myr assuming a jet-head velocity of 0.1c). Radio activity seems to be a short-lived process in active galaxies, although in some cases recurrent: five objects in our sample present signs of reactivation in their radio structures.