The influence of Massive Black Hole Binaries on the Morphology of Merger Remnants

Bortolas, Elisa, Gualandris, Alessia, Dotti, Massimo and Read, Justin I. (2018) The influence of Massive Black Hole Binaries on the Morphology of Merger Remnants Monthly Notices of the Royal Astronomical Society, 477 (2). pp. 2310-2325.

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Abstract

Massive black hole (MBH) binaries, formed as a result of galaxy mergers, are expected to harden by dynamical friction and three-body stellar scatterings, until emission of gravitational waves (GWs) leads to their final coalescence. According to recent simulations, MBH binaries can efficiently harden via stellar encounters only when the host geometry is triaxial, even if only modestly, as angular momentum diffusion allows an efficient repopulation of the binary loss cone. In this paper, we carry out a suite of N-body simulations of equal-mass galaxy collisions, varying the initial orbits and density profiles for the merging galaxies and running simulations both with and without central MBHs. We find that the presence of an MBH binary in the remnant makes the system nearly oblate, aligned with the galaxy merger plane, within a radius enclosing 100 MBH masses. We never find binary hosts to be prolate on any scale. The decaying MBHs slightly enhance the tangential anisotropy in the centre of the remnant due to angular momentum injection and the slingshot ejection of stars on nearly radial orbits. This latter effect results in about 1% of the remnant stars being expelled from the galactic nucleus. Finally, we do not find any strong connection between the remnant morphology and the binary hardening rate, which depends only on the inner density slope of the remnant galaxy. Our results suggest that MBH binaries are able to coalesce within a few Gyr, even if the binary is found to partially erase the merger-induced triaxiality from the remnant.

Item Type:	Article
Divisions :	Faculty of Engineering and Physical Sciences > Physics
Authors :	Name Email ORCID Bortolas, Elisa Gualandris, Alessia a.gualandris@surrey.ac.uk Dotti, Massimo Read, Justin I.
Date :	2018
DOI :	10.1093/mnras/sty775
Copyright Disclaimer :	© 2018 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/about_us/legal/notices)
Uncontrolled Keywords :	Black hole physics. Gravitational waves. Methods: numerical. Galaxies: interactions. Galaxies: kinematics and dynamics. Galaxies: structure.
Related URLs :	https://academic.oup.com/mnras
Depositing User :	Clive Harris
Date Deposited :	28 Mar 2018 14:41
Last Modified :	16 Jan 2019 19:08
URI:	http://epubs.surrey.ac.uk/id/eprint/846106

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