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Nuclear coups: dynamics of black holes in galaxy mergers


Van Wassenhove, S; Capelo, P R; Volonteri, M; Dotti, M; Bellovary, J M; Mayer, L; Governato, F (2014). Nuclear coups: dynamics of black holes in galaxy mergers. Monthly Notices of the Royal Astronomical Society, 439(1):474-487.

Abstract

We study the dynamical evolution of supermassive black holes (BHs) in merging galaxies on scales of hundreds of kpc to 10 pc, to identify the physical processes that aid or hinder the orbital decay of BHs. We present hydrodynamical simulations of galaxy mergers with a resolution of ≤20 pc, chosen to accurately track the motion of the nuclei and provide a realistic environment for the evolution of the BHs. We find that, during the late stages of the merger, tidal shocks inject energy in the nuclei, causing one or both nuclei to be disrupted and leaving their BH `naked', without any bound gas or stars. In many cases, the nucleus that is ultimately disrupted is that of the larger galaxy (`nuclear coup'), as star formation grows a denser nuclear cusp in the smaller galaxy. We supplement our simulations with an analytical estimate of the orbital-decay time required for the BHs to form a binary at unresolved scales, due to dynamical friction. We find that, when a nuclear coup occurs, the time-scale is much shorter than when the secondary's nucleus is disrupted, as the infalling BH is more massive, and it also finds itself in a denser stellar environment.

Abstract

We study the dynamical evolution of supermassive black holes (BHs) in merging galaxies on scales of hundreds of kpc to 10 pc, to identify the physical processes that aid or hinder the orbital decay of BHs. We present hydrodynamical simulations of galaxy mergers with a resolution of ≤20 pc, chosen to accurately track the motion of the nuclei and provide a realistic environment for the evolution of the BHs. We find that, during the late stages of the merger, tidal shocks inject energy in the nuclei, causing one or both nuclei to be disrupted and leaving their BH `naked', without any bound gas or stars. In many cases, the nucleus that is ultimately disrupted is that of the larger galaxy (`nuclear coup'), as star formation grows a denser nuclear cusp in the smaller galaxy. We supplement our simulations with an analytical estimate of the orbital-decay time required for the BHs to form a binary at unresolved scales, due to dynamical friction. We find that, when a nuclear coup occurs, the time-scale is much shorter than when the secondary's nucleus is disrupted, as the infalling BH is more massive, and it also finds itself in a denser stellar environment.

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Institute for Computational Science
Dewey Decimal Classification:530 Physics
Language:English
Date:March 2014
Deposited On:13 Aug 2014 14:47
Last Modified:05 Apr 2016 18:01
Publisher:Oxford University Press
ISSN:0035-8711
Free access at:Publisher DOI. An embargo period may apply.
Publisher DOI:https://doi.org/10.1093/mnras/stu024

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