Speaker
Description
Aims. The origin of the morphological dichotomy between Fanaroff–Riley Class I (FRI) and Class II (FRII) radio galaxies has long
been debated, and some theories propose that it may be influenced by their environments. In this study, we use galaxy clusters as
tracers of environment to investigate whether environmental conditions play a significant role in shaping the FRI/FRII classification.
Methods. Using the LoTSS DR2 FRI/FRII catalogue, we construct two samples: a volume-limited sample and a paired sample, where
each FRII is matched to the nearest FRI in luminosity and redshift. We investigate the environmental properties of FRIs and FRIIs by
cross-matching them with a galaxy cluster catalogue, which identifies clusters based on the overdensity of stellar mass in the DESI
Legacy Imaging Surveys.
Results. We find that FRIs are more frequently located in galaxy clusters than FRIIs, particularly at high radio luminosities where
the cluster association of FRIIs drops significantly. However, once inside clusters, the two populations exhibit similar environmental
properties. In particular, the richness and M500 values of host clusters are comparable, and both FRI and FRII sources show nearly
identical radial density profiles, peaking at 0.5 × R500 and declining beyond R500. Furthermore, the likelihood of a radio galaxy being
the brightest cluster galaxy (BCG) is similarly high for both classes, with no significant differences in the properties of FRI-BCGs
and FRII-BCGs or their host clusters.
Conclusions. Our findings support a scenario in which the large-scale environments of FRIs and FRIIs are broadly similar once they
reside in clusters. The observed morphological dichotomy is unlikely to be driven solely by galaxy cluster properties, and may instead
reflect host-scale processes.
