A Caltech Library Service

Why are active galactic nuclei and host galaxies misaligned?

Hopkins, Philip F. and Hernquist, Lars and Hayward, Christopher C. and Narayanan, Desika (2012) Why are active galactic nuclei and host galaxies misaligned? Monthly Notices of the Royal Astronomical Society, 425 (2). pp. 1121-1128. ISSN 0035-8711.

[img] PDF - Published Version
See Usage Policy.

[img] PDF - Accepted Version
See Usage Policy.


Use this Persistent URL to link to this item:


It is well established observationally that the characteristic angular momentum axis on small scales around active galactic nuclei (AGN), traced by radio jets and the putative torus, is not well correlated with the large-scale angular momentum axis of the host galaxy. In this paper, we show that such misalignments arise naturally in high-resolution simulations in which we follow angular momentum transport and inflows from galaxy to sub-pc scales near AGN, triggered either during galaxy mergers or by instabilities in isolated discs. Sudden misalignments can sometimes be caused by single massive clumps falling into the centre slightly off-axis, but more generally, they arise even when the gas inflows are smooth and trace only global gravitational instabilities. When several nested, self-gravitating modes are present, the inner ones can precess and tumble in the potential of the outer modes. Resonant angular momentum exchange can flip or re-align the spin of an inner mode on a short time-scale, even without the presence of massive clumps. We therefore do not expect that AGN and their host galaxies will be preferentially aligned, nor should the relative alignment be an indicator of the AGN fuelling mechanism. We discuss implications of this conclusion for AGN feedback and black hole (BH) spin evolution. The misalignments may mean that even BHs accreting from smooth large-scale discs will not be spun up to maximal rotation and so have more modest radiative efficiencies and inefficient jet formation. Even more random orientations/lower spins are possible if there is further unresolved clumpiness in the gas, and more ordered accretion may occur if the inflow is slower and not self-gravitating.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Hopkins, Philip F.0000-0003-3729-1684
Hernquist, Lars0000-0001-6950-1629
Hayward, Christopher C.0000-0003-4073-3236
Narayanan, Desika0000-0002-7064-4309
Alternate Title:Why Are AGN and Host Galaxies Misaligned?
Additional Information:© 2012 The Authors. Monthly Notices of the Royal Astronomical Society © 2012 RAS. Accepted 2012 June 7. Received 2012 May 23; in original form 2011 November 1. We thank Massimo Dotti and the anonymous referee for comments and suggestions that greatly improved this paper, in particular in the discussion of BH spin. We also thank Eliot Quataert and Robert Antonucci for helpful discussions in the development of this work. Support for PFH was provided by NASA through Einstein Postdoctoral Fellowship Award Number PF1-120083. DN acknowledges support from the NSF via grant AST-1009452.
Funding AgencyGrant Number
NASA Einstein FellowshipPF1-120083
Subject Keywords:galaxies: active, galaxies: evolution, quasars: general, cosmology: theory
Issue or Number:2
Record Number:CaltechAUTHORS:20200601-143024713
Persistent URL:
Official Citation:Philip F. Hopkins, Lars Hernquist, Christopher C. Hayward, Desika Narayanan, Why are active galactic nuclei and host galaxies misaligned?, Monthly Notices of the Royal Astronomical Society, Volume 425, Issue 2, September 2012, Pages 1121–1128,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:103614
Deposited By: George Porter
Deposited On:01 Jun 2020 22:29
Last Modified:01 Jun 2020 22:29

Repository Staff Only: item control page