Title:	The abundance of x-shaped radio sources: implications for the gravitational wave background
Authors:	Roberts, David H Saripalli, Lakshmi Subrahmanyan, Ravi
Keywords:	Radio Continuum
Issue Date:	Sep-2015
Publisher:	2015 American Astronomical Society
Citation:	Astrophysical Journal Letters, 2015, Vol. 810, L6
Abstract:	Coalescence of supermassive black holes (SMBHs) in galaxy mergers is potentially the dominant contributor to the low frequency gravitational wave background (GWB). It was proposed by Merritt & Ekers that X-shaped radio galaxies are signposts of such coalescences and that their abundance might be used to predict the magnitude of the GWB. In Roberts et al. we presented radio images of all 52 X-shaped radio source candidates out of the sample of 100 selected by Cheung for which archival VLA data were available. These images indicate that at most 21% of the candidates might be genuine X-shaped radio sources that were formed by a restarting of beams in a new direction following a major merger. This suggests that fewer than 1.3% of extended radio sources appear to be candidates for genuine axis reorientations ("spin flips"), much smaller than the 7% suggested by Leahy & Parma. Thus, the associated GWB may be substantially smaller than previous estimates. These results can be used to normalize detailed calculations of the SMBH coalescence rate and the GWB.
Description:	Restricted Access. An open-acce s version is available at arXiv.org (one of the alternative locations)
URI:	http://hdl.handle.net/2289/6345
ISSN:	2041-8213 (Online) 2041-8205
Alternative Location:	http://adsabs.harvard.edu/abs/2015ApJ...810L...6R http://arxiv.org/abs/1503.02021 http://dx.doi.org/10.1088/2041-8205/810/1/L6
Copyright:	2015 American Astronomical Society
Appears in Collections:	Research Papers (A&A)

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