Catching butterflies in the sky: Extended catalog of winged or X-shaped radio sources from the latest FIRST data release. (arXiv:1905.06356v1 [astro-ph.HE])

Catching butterflies in the sky: Extended catalog of winged or X-shaped radio sources from the latest FIRST data release. (arXiv:1905.06356v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Yang_X/0/1/0/all/0/1">Xiaolong Yang</a> (KIAA-PKU), <a href="http://arxiv.org/find/astro-ph/1/au:+Joshi_R/0/1/0/all/0/1">Ravi Joshi</a> (KIAA-PKU), <a href="http://arxiv.org/find/astro-ph/1/au:+Gopal-Krishna/0/1/0/all/0/1">Gopal-Krishna</a> (ARIES), <a href="http://arxiv.org/find/astro-ph/1/au:+An_T/0/1/0/all/0/1">Tao An</a> (SHAO), <a href="http://arxiv.org/find/astro-ph/1/au:+Ho_L/0/1/0/all/0/1">Luis C. Ho</a> (KIAA-PKU), <a href="http://arxiv.org/find/astro-ph/1/au:+Wiita_P/0/1/0/all/0/1">Paul J. Wiita</a> (TCNJ), <a href="http://arxiv.org/find/astro-ph/1/au:+Liu_X/0/1/0/all/0/1">Xiang Liu</a> (XAO), <a href="http://arxiv.org/find/astro-ph/1/au:+Yang_J/0/1/0/all/0/1">Jun Yang</a> (OSO), <a href="http://arxiv.org/find/astro-ph/1/au:+Wang_R/0/1/0/all/0/1">Ran Wang</a> (KIAA-PKU), <a href="http://arxiv.org/find/astro-ph/1/au:+Wu_X/0/1/0/all/0/1">Xuebing Wu</a> (KIAA-PKU), <a href="http://arxiv.org/find/astro-ph/1/au:+Yang_X/0/1/0/all/0/1">Xiaofeng Yang</a> (XAO)

We present a catalog of 290 `winged’ or X-shaped radio galaxies (XRGs)
extracted from the latest (17 Dec. 2014) data release of the `Very Large Array
Faint Images of the Radio Sky at Twenty centimeter’ (VLA FIRST survey). We have
combined these radio images with their counterparts in the TIFR GMRT sky survey
(TGSS) at 150 MHz (TGSS alternative data release, TGSS_ADR1), 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 must be verified by further
observations. The present sample of 290 XRG candidates is almost twice as large
as the number of XRGs presently 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
(2 `strong’ and 1 `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 GHz 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.

We present a catalog of 290 `winged’ or X-shaped radio galaxies (XRGs)
extracted from the latest (17 Dec. 2014) data release of the `Very Large Array
Faint Images of the Radio Sky at Twenty centimeter’ (VLA FIRST survey). We have
combined these radio images with their counterparts in the TIFR GMRT sky survey
(TGSS) at 150 MHz (TGSS alternative data release, TGSS_ADR1), 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 must be verified by further
observations. The present sample of 290 XRG candidates is almost twice as large
as the number of XRGs presently 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
(2 `strong’ and 1 `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 GHz 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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