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Abstract In pursuit of clues to the origin of “winged” or X-shaped radio galaxies (XRGs) we investigate the parent galaxies of a large sample of 106 XRGs for optical–radio axes alignment, interstellar medium, black hole mass, and large-scale environment. For 41 of the XRGs it was possible to determine the optical major axis and the primary radio axis and the strong tendency for the two axes to be fairly close is confirmed. However, several counter-examples were also found and these could challenge the widely discussed backflow diversion model for the origin of the radio wings. Comparison with a well-defined large sample of normal FR II radio galaxies has revealed that: (i) XRGs possess slightly less massive central black holes than the normal radio galaxies (average masses being logM BH ∼ 8.81 M ⊙ and 9.07 M ⊙, respectively); (ii) a much higher fraction of XRGs (∼80%) exhibits red mid-IR colors (W2 − W3 > 1.5), indicating a population of young stars and/or an enhanced dust mass, probably due to relatively recent galaxy merger(s). A comparison of the large-scale environment (i.e., within ∼1 Mpc) shows that both XRGs and FRII radio galaxies inhabit similarly poor galaxy clustering environments (medium richness being 8.94 and 11.87, respectively). Overall, the origin of XRGs seems difficult to reconcile with a single dominant physical mechanism and competing mechanisms seem prevalent.
High Energy Astrophysical Phenomena (astro-ph.HE), Astrophysics of Galaxies (astro-ph.GA), FOS: Physical sciences, Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Astrophysics of Galaxies
High Energy Astrophysical Phenomena (astro-ph.HE), Astrophysics of Galaxies (astro-ph.GA), FOS: Physical sciences, Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Astrophysics of Galaxies
citations This is an alternative to the "Influence" indicator, which also reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically). | 19 | |
popularity This indicator reflects the "current" impact/attention (the "hype") of an article in the research community at large, based on the underlying citation network. | Top 10% | |
influence This indicator reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically). | Average | |
impulse This indicator reflects the initial momentum of an article directly after its publication, based on the underlying citation network. | Top 10% |