Radio-loud AGN morphology and host-galaxy properties in the LOFAR Two-Metre Sky Survey Data Release 2

TL;DR

This study introduces a new semi-automated classification method for radio-loud AGN morphologies using LOFAR data, revealing complex influences of host galaxy properties and environment on FR classifications.

Contribution

A novel semi-automated method for classifying RLAGN morphology and a large, publicly available catalogue based on LOFAR data, reassessing the FR divide and its physical drivers.

Findings

RLAGN near the FR divide with certain luminosities are more likely to be FRI in massive hosts.

No clear correlation between FR break luminosity and stellar mass or host magnitude.

Inner environment may influence jet disruption and morphology.

Abstract

Radio-loud active galaxies (RLAGN) can exhibit various morphologies. The Fanaroff-Riley (FR) classifications, which are defined by the locations of peaks in surface brightness, have been applied to many catalogues of RLAGN. The FR classifications were initially found to correlate with radio luminosity. However, recent surveys have demonstrated that radio luminosity alone does not reliably predict radio morphology. We have devised a new-semi automated method involving ridgeline characterisations to compile the largest known classified catalogue of RLAGN to date with data from the second data release of the LOFAR Two-Metre Sky Survey (LoTSS DR2). We reassess the FR divide and its cause by examining the physical and host galaxy properties of $3590$ FRIIs and $2354$ FRIs (at $z \leq 0.8$). We find that RLAGN near the FR divide with $10^{25} \le L_{144} \le 10^{26} $ WHz$^{-1}$ are more likely to show FRI over FRII morphology if they occupy more massive host galaxies. We find no correlation, when considering selection effects, between the FR break luminosity and stellar mass or host-galaxy rest-frame absolute magnitude. Overall, we find the cause of different radio morphologies in this sample to be complex. Considering sources near the FR divide with $10^{25} \le L_{144} \le 10^{26} $ WHz$^{-1}$, we find evidence to support inner environment having a role in determining jet disruption. We make available a public catalogue of morphologies for our sample, which will be of use for future investigations of RLAGN and their impact on their surroundings.