Probing the environments of FRI and FRII radio galaxies in LoTSS DR2 with galaxy clusters

Aims. The origin of the morphological dichotomy between Fanaroff-Riley Class I (FRI) and Class II (FRII) radio galaxies has long been debated. In this study, we investigate whether the cluster-scale environment plays a significant role in shaping the morphology of FRIs and FRIIs. Methods. Using the new morphologically classified catalogue from the second data release of the LOFAR Two-metre Sky Survey (LoTSS DR2), we construct two samples at z < 0.4: a volume-limited sample with L 144 > 4 × 10 24 W Hz −1 and a paired sample in which each FRII is matched to the nearest FRI in luminosity and redshift. We cross-match these samples with a recent galaxy cluster catalogue based on the DESI Legacy Imaging Survey. A galaxy is considered associated with a cluster with M 500  > 0.47 × 10 14  M ⊙ if the redshift difference between the galaxy and the cluster centre is below 0.01, and the projected distance between the two is smaller than 2R 500. Results. In the volume-limited sample, 48.6 −1.8 +1.8% of FRIs and 30.6 −2.3 +2.5% of FRIIs are associated with clusters. In the paired sample, 45.6 −3.1 +3.1% of FRIs and 32.6 −2.8 +3.0% of FRIIs are associated with clusters. This difference in cluster match fractions between FRIs and FRIIs in both samples becomes more pronounced at higher radio luminosities (L 144 MHz > 10 26 W Hz −1). In the volume-limited sample, 55.6 −9.6 +9.2% of luminous FRIs and 19.0 −4.6 +5.7% of luminous FRIIs are associated with clusters. In the paired sample, 50.0 −12.9 +12.9% of luminous FRIs and 6.7 −3.9 +9.5% of luminous FRIIs are associated with clusters. Nevertheless, those FRIs and FRIIs that are associated with clusters show similar properties. In particular, the distributions of radio luminosity and stellar mass as functions of cluster richness and M 500 are similar for FRIs and FRIIs. The radial density profiles of cluster-associated FRIs and FRIIs both peak at 0.5 × R 500 and decline beyond R 500, showing very similar spatial distributions within clusters. Furthermore, in the volume-limited sample, 74.8 −2.3 +2.2% of cluster-associated FRIs and 61.9 −4.6 +4.4% of cluster-associated FRIIs are identified as brightest cluster galaxies (BCGs). In the paired sample, 78.1 −4.0 +3.5% of cluster-associated FRIs and 65.9 −5.3 +4.9% of cluster-associated FRIIs are identified as BCGs. The median properties of these FRI-BCGs and FRII-BCGs, as well as those of their host clusters, do not show significant differences. Conclusions. Compared to FRIs, FRIIs are less frequently found in galaxy clusters, particularly at high radio luminosities. This pattern may be explained by the jet disruption scenario, in which the dense gas in galaxy clusters can slow down or disturb radio jets, making it more difficult for powerful FRII structures to form or remain stable. However, when FRIs and FRIIs do reside in clusters, they appear to inhabit similar environments in terms of richness, mass, and radial position. These findings suggest that, while the cluster-scale environment may influence the cluster match fraction, the morphological distinction between FRIs and FRIIs is unlikely to be primarily driven by cluster-scale properties alone. Improved estimates of cluster richness and mass will help to further clarify the extent to which the cluster environment influences the radio morphology of FRIs and FRIIs.