Catching butterflies in the sky: Extended catalog of winged or X-shaped radio sources from the latest FIRST data release

Kavli Affiliate: Xuebing Wu

| First 5 Authors: Xiaolong Yang, Ravi Joshi, Gopal-Krishna, Tao An, Luis C. Ho

| Summary:

We present a catalog of 290 "winged" or X-shaped radio galaxies (XRGs)
extracted from the latest (2014 December 17) data release of the "Very Large
Array Faint Images of the Radio Sky at Twenty centimeter." We have combined
these radio images with their counterparts in the TIFR GMRT sky survey at 150
MHz, in an attempt to identify any low surface brightness radio emission
present in these sources. This has enabled us to assemble a sample of 106
"strong" XRG candidates and 184 "probable" XRG candidates whose XRG designation
needs to be verified by further observations. The present sample of 290 XRG
candidates is almost twice as large as the number of XRGs currently known.
Twenty-five of our 290 XRG candidates (9 "strong" and 16 "probable") are
identified as quasars. Double-peaked narrow emission lines are seen in the
optical spectra of three of the XRG candidates (two "strong" and one
"probable"). Nearly 90% of the sample is located in the FR II domain of the
Owen-Ledlow diagram. A few of the strong XRG candidates have a rather flat
radio spectrum (spectral index alpha flatter than -0.3) between 150 MHz and 1.4
GHz, or between 1.4 and 5 GHz. Since this is not expected for lobe-dominated
extragalactic radio sources (like nearly all known XRGs), these sources are
particularly suited for follow-up radio imaging and near-simultaneous
measurement of the radio spectrum.

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