Revisiting the Fanaroff–Riley dichotomy and radio-galaxy morphology with the LOFAR Two-Metre Sky Survey (LoTSS)
2019
The relative positions of the high and low
surface brightnessregions of radio-
loudactive galaxies in the 3CR sample were found by Fanaroff and Riley to be correlated with their
luminosity. We revisit this canonical relationship with a sample of 5805 extended radio-
loudAGN from the
LOFARTwo-Metre Sky Survey (LoTSS), compiling the most complete dataset of
radio-galaxymorphological information obtained to date. We demonstrate that, for this sample, radio
luminositydoes *not* reliably predict whether a source is edge-brightened (FRII) or centre-brightened (FRI). We highlight a large population of low-
luminosityFRIIs, extending three orders of magnitude below the traditional FR break, and demonstrate that their host galaxies are on average systematically fainter than those of high-
luminosityFRIIs and of FRIs matched in
luminosity. This result supports the jet power/environment paradigm for the FR break: low-power jets may remain undisrupted and form hotspots in lower mass hosts. We also find substantial populations that appear physically distinct from the traditional FR classes, including candidate restarting sources and ``hybrids''. We identify 459 bent-tailed sources, which we find to have a significantly higher SDSS cluster association fraction (at $z<0.4$) than the general
radio-galaxypopulation, similar to the results of previous work. The complexity of the LoTSS faint, extended radio sources demonstrates the need for caution in the automated classification and interpretation of extended sources in modern radio surveys, but also reveals the wealth of morphological information such surveys will provide and its value for advancing our physical understanding of radio-
loudAGN.
Keywords:
-
Correction
-
Source
-
Cite
-
Save
141
References
88
Citations
NaN
KQI