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Seeds Don't Sink: Even Massive Black Hole "Seeds" Cannot Migrate to Galaxy Centers Efficiently

Ma, Linhao and Hopkins, Philip F. and Ma, Xiangcheng and Anglés-Alcázar, Daniel and Faucher-Giguère, Claude-André and Kelley, Luke Zoltan (2021) Seeds Don't Sink: Even Massive Black Hole "Seeds" Cannot Migrate to Galaxy Centers Efficiently. . (Unpublished)

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Possible formation scenarios of supermassive black holes (SMBHs) in the early universe include rapid growth from less massive seed black holes (BHs) via super-Eddington accretion or runaway mergers, yet both of these scenarios would require seed BHs to efficiently sink to and be trapped in the galactic center via dynamical friction (DF). This may not be true for their complicated dynamics in clumpy high-z galaxies. In this work we study this "sinking problem" with state-of-the-art high-resolution cosmological simulations, combined with both direct N-body integration of seed BH trajectories and post-processing of randomly generated test particles with a newly developed DF estimator. We find that seed BHs less massive than 10⁸M⊙ (i.e., all but the already-supermassive seeds) cannot efficiently sink in typical high-z galaxies. We also discuss two possible solutions: forming a huge number of seeds such that one can end up trapped in the galactic center by chance, or seed BHs being embedded in giant structures (e.g. star clusters) with huge effective masses above the mass threshold. We discuss the limitations of both solutions.

Item Type:Report or Paper (Discussion Paper)
Related URLs:
URLURL TypeDescription Paper
Hopkins, Philip F.0000-0003-3729-1684
Ma, Xiangcheng0000-0001-8091-2349
Anglés-Alcázar, Daniel0000-0001-5769-4945
Faucher-Giguère, Claude-André0000-0002-4900-6628
Kelley, Luke Zoltan0000-0002-6625-6450
Additional Information:We thank Zuyi Chen and Alessandro Lupi for useful discussions. Support for LM & PFH was provided by NSF Research Grants 1911233 & 20009234, NSF CAREER grant 1455342, NASA grants 80NSSC18K0562, HST-AR-15800.001-A. DAA acknowledges support by NSF grant AST-2009687 and by the Flatiron Institute, which is supported by the Simons Foundation. CAFG was supported by NSF through grants AST-1715216 and CAREER award AST-1652522; by NASA through grant 17-ATP17-0067; and by a Cottrell Scholar Award and a Scialog Award from the Research Corporation for Science Advancement. Numerical calculations were run on the Caltech compute cluster “Wheeler,” allocations FTA-Hopkins supported by the NSF and TACC, and NASA HEC SMD-16-7592. Data Availability: The data and source code supporting the plots within this article are available on reasonable request to the corresponding author.
Group:Astronomy Department, TAPIR
Funding AgencyGrant Number
Flatiron InstituteUNSPECIFIED
Simons FoundationUNSPECIFIED
Cottrell Scholar of Research CorporationUNSPECIFIED
Subject Keywords:black hole physics – galaxies: kinematics and dynamics – galaxies: formation – galaxies: evolution – galaxies: high-redshift – quasars: supermassive black holes
Record Number:CaltechAUTHORS:20210309-082003361
Persistent URL:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:108359
Deposited By: Tony Diaz
Deposited On:10 Mar 2021 20:06
Last Modified:10 Mar 2021 20:06

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