2007AJ....133.2097C

A small number of double-lobed radio galaxies (17 from our own census of the literature) show an additional pair of low surface brightness ``wings'', thus forming an overall X-shaped appearance. The origin of the wings in these radio sources is unclear. They may be the result of backflowing plasma from the currently active radio lobes into an asymmetric medium surrounding the active nucleus, which would make these ideal systems in which to study thermal/nonthermal plasma interactions in extragalactic radio sources. Another possibility is that the wings are the aging radio lobes left over after a (rapid) realignment of the central supermassive black hole-accretion disk system due perhaps to a merger. Generally, these models are not well tested; with the small number of known examples, previous works have focused on detailed case studies of selected sources with little attempt at a systematic study of a large sample. Using the VLA FIRST survey database, we are compiling a large sample of winged and X-shaped radio sources for such studies. As a first step toward this goal, an initial sample of 100 new candidate objects of this type are presented in this paper. The search process is described, and optical identifications from available literature data and basic radio data are presented. From the limited-resolution FIRST images (∼5"), we can already confidently classify a sufficient number of these objects as having the characteristic wing lengths of >80% of the active lobes to more than double the number of known X-shaped radio sources. We have also included as candidates radio sources with shorter wings (<80% wing-to-lobe length ratios), or simply ``winged'' sources, as it is probable that projection effects are important. Finally, among the candidates are four quasars (z=0.37-0.84), and several have morphologies suggestive of Fanaroff-Riley type I (low-power) radio galaxies. While follow-up observations are necessary to confirm these identifications, this stresses the importance of source orientation and imaging limitations in finding these enigmatic objects.