The abundance of X-shaped radio sources. I. VLA survey of 52 sources with off-axis distortions

Abstract

Cheung identified a sample of 100 candidate X-shaped radio galaxies using the NRAO FIRST survey; these are small-axial-ratio extended radio sources with off-axis emission. Here, we present radio images of 52 of these sources that have been made from archival Very Large Array data with resolution of about 1''. Fifty-one of the 52 were observed at 1.4 GHz, 7 were observed at 1.4 and 5 GHz and 1 was observed only at 5 GHz. We also present overlays of the Sloan Digital Sky Survey red images for 48 of the sources and DSS II overlays for the remainder. Optical counterparts have been identified for most sources, but there remain a few empty fields. Our higher resolution VLA images along with FIRST survey images of the sources in the sample reveal that extended extragalactic radio sources with small axial ratios are largely (60%) cases of double radio sources with twin lobes that have off-axis extensions, usually with inversion-symmetric structure. The available radio images indicate that at most 20% of sources might be genuine X-shaped radio sources that could have formed by a restarting of beams in a new direction following an interruption and axis flip. The remaining 20% are in neither of these categories. The implications of this result for the gravitational wave background are discussed in Roberts et al.