A Caltech Library Service

Why do black holes trace bulges (& central surface densities), instead of galaxies as a whole?

Hopkins, Philip F. and Wellons, Sarah and Anglés-Alcázar, Daniel and Faucher-Giguère, Claude-André and Grudić, Michael Y. (2022) Why do black holes trace bulges (& central surface densities), instead of galaxies as a whole? Monthly Notices of the Royal Astronomical Society, 510 (1). pp. 630-638. ISSN 0035-8711. doi:10.1093/mnras/stab3458.

[img] PDF - Published Version
See Usage Policy.

[img] PDF - Submitted Version
See Usage Policy.


Use this Persistent URL to link to this item:


Previous studies of fueling black holes in galactic nuclei have argued (on scales ∼0.01−1000pc) accretion is dynamical with inflow rates M˙∼ηM_(gas)/t_(dyn) in terms of gas mass M_(gas), dynamical time t_(dyn), and some η. But these models generally neglected expulsion of gas by stellar feedback, or considered extremely high densities where expulsion is inefficient. Studies of star formation, however, have shown on sub-kpc scales the expulsion efficiency f_(wind) = M_(ejected)/M_(total) scales with the gravitational acceleration as (1−f_(wind))/f_(wind)∼a¯_(grav)/⟨p˙/m∗⟩∼Σ_(eff)/Σ_(crit) where a¯_(grav) ≡ GM_(tot)(<r)/r² and ⟨p˙/m∗⟩ is the momentum injection rate from young stars. Adopting this as the simplest correction for stellar feedback, η → η(1−f_(wind))⁠, we show this provides a more accurate description of simulations with stellar feedback at low densities. This has immediate consequences, predicting the slope and normalization of the M_(BH) − σ and M_(BH) – M_(bulge) relation, L_(AGN) −SFR relations, and explanations for outliers in compact Es. Most strikingly, because star formation simulations show expulsion is efficient (f_(wind) ∼ 1) below total-mass surface density M_(tot)/πr² < Σ_(crit)∼3 × 10⁹ M⊙ kpc⁻² (where Σ_(crit) = ⟨p˙/m∗⟩/(πG), BH mass is predicted to specifically trace host galaxy properties above a critical surface brightness Σ_(crit) (B-band μ_(crit)_B ∼19 mag arcsec⁻²⁠). This naturally explains why BH masses preferentially reflect bulge properties or central surface densities (e.g. Σ_(1kpc)⁠), not ‘total’ galaxy properties.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper ItemGIZMO code
Hopkins, Philip F.0000-0003-3729-1684
Wellons, Sarah0000-0002-3977-2724
Anglés-Alcázar, Daniel0000-0001-5769-4945
Faucher-Giguère, Claude-André0000-0002-4900-6628
Grudić, Michael Y.0000-0002-1655-5604
Additional Information:© 2021 The Author(s). Published by Oxford University Press on behalf of Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model ( Accepted 2021 No v ember 25. Received 2021 October 26; in original form 2021 March 15. Published: 29 November 2021. We thank Jessie Christiansen, Michael Fall, Peter Mitchell, Guang Yang, and our anonymous referee for a number of helpful suggestions and insightful comments. Support for PFH was provided by NSF Research Grants 1911233 & 20009234, NSF CAREER grant 1455342, NASA grants 80NSSC18K0562, HST-AR-15800.001-A. SW is supported by an NSF Astronomy and Astrophysics Postdoctoral Fellowship under award AST2001905. CAFG was supported by NSF through grants AST-1715216 and CAREER award AST-1652522; by NASA through grant 17-ATP17-0067; by STScI through grant HST-AR-16124.001-A; and by the Research Corporation for Science Advancement through a Cottrell Scholar Award and a Scialog Award. 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 Statement: The data supporting the plots within this article are available on reasonable request to the corresponding author. A public version of the GIZMO code is available at
Group:Astronomy Department, TAPIR
Funding AgencyGrant Number
Cottrell Scholar of Research CorporationUNSPECIFIED
Scialog Fellow of Research CorporationUNSPECIFIED
Subject Keywords:accretion, accretion discs – galaxies: active – galaxies: evolution – galaxies: formation – quasars: general – quasars: supermassive black holes
Issue or Number:1
Record Number:CaltechAUTHORS:20210323-124505549
Persistent URL:
Official Citation:Philip F Hopkins, Sarah Wellons, Daniel Anglés-Alcázar, Claude-André Faucher-Giguère, Michael Y Grudić, Why do black holes trace bulges (& central surface densities), instead of galaxies as a whole?, Monthly Notices of the Royal Astronomical Society, Volume 510, Issue 1, February 2022, Pages 630–638,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:108528
Deposited By: Tony Diaz
Deposited On:23 Mar 2021 20:55
Last Modified:24 Jan 2022 20:55

Repository Staff Only: item control page