X-shaped radio galaxies and the nanohertz gravitational wave background

Roberts, David H. ; Saripalli, Lakshmi ; Subrahmanyan, Ravi (2015) X-shaped radio galaxies and the nanohertz gravitational wave background Proceedings of the International Astronomical Union, 11 (A29B). pp. 319-320. ISSN 1743-9213

Full text not available from this repository.

Official URL: https://www.cambridge.org/core/journals/proceeding...

Related URL: http://dx.doi.org/10.1017/S1743921316005445

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. Cheung identified a sample of 100 candidate X-shaped radio galaxies using the NRAO FIRST survey; these are small-axial-ratio extended radio sources with off-axis emission. In Roberts et al. we made radio images of 52 of these sources with resolution of about 1 arcsecond using archival Very Large Array data. Fifty-one of the 52 were observed at 1.4 GHz, seven were observed at 1.4 and 5 GHz and one was observed only at 5 GHz. Our higher resolution VLA images along with FIRST survey images of the sources in the sample reveal that extended extragalactic radio sources with small axial ratios are largely (60%) cases of double radio sources with twin lobes that have off-axis extensions, usually with inversion-symmetric structure. The available radio images indicate that at most 20% of sources might be genuine X-shaped radio sources that could have formed by a restarting of beams in a new direction following an interruption and axis flip. The remaining 20% are in neither of these categories. These images indicate that at most a small fraction 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, or by spin drift caused by BH-BH interaction. This suggests that fewer than 1.3% of extended radio sources appear to be candidates for genuine axis reorientations (“spin flips”) or 2.2% if possible “axis drift” sources are included, 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.

Item Type:Article
Source:Copyright of this article belongs to Cambridge University Press.
Keywords:Gravitational Wave Background; Radio Galaxies; Supermassive Black Holes
ID Code:114240
Deposited On:22 May 2018 04:52
Last Modified:22 May 2018 04:52

Repository Staff Only: item control page