FIRST "Winged" and X-Shaped Radio Source Candidates

A small number of double-lobed radio galaxies (17 from our own census of theliterature) show an additional pair of low surface brightness `wings', thusforming an overall `X'-shaped appearance. The origin of the wings in theseradio sources is unclear. They may be the result of back-flowing plasma fromthe currently active radio lobes into an asymmetric medium surrounding theactive nucleus, which would make these ideal systems in which to studythermal/non-thermal plasma interactions in extragalactic radio sources. Anotherpossibility is that the wings are the aging radio lobes left over after a(rapid) realignment of the central supermassive black-hole/accretion disksystem due perhaps to a merger. Generally, these models are not well tested;with the small number of known examples, previous works focused on detailedcase studies of selected sources with little attempt at a systematic study of alarge sample. Using the VLA-FIRST survey database, we are compiling a largesample of winged and X-shaped radio sources for such studies. As a first steptoward this goal, an initial sample of 100 new candidate objects of this typeare presented in this paper. ...[abridged]