Black holes and galactic density cusps

Spherically symmetric anisotropic cusps

¹ Instituto de Física Teórica UAM/CSIC, Facultad de Ciencias, C-XI, Universidad Autónoma de Madrid, Cantoblanco, 28049 Madrid, Spain
e-mail: Morgan.LeDelliou@uam.es
² Queen’s University, Kingston, Ontario, Canada
e-mail: henriksn@astro.queensu.ca
³ Faculty of Science, University of Ontario Institute of Technology, Oshawa, Ontario, L1H 7K4, Canada
e-mail: joseph.macmillan@gmail.com

Received: 11 November 2009
Accepted: 20 February 2010

Abstract

Aims. In this paper we study density cusps that may contain central black holes. The actual co-eval self-similar growth would not distinguish between the central object and the surroundings.

Methods. To study the environment of a growing black hole we seek descriptions of steady “cusps” that may contain a black hole and that retain at least a memory of self-similarity. We refer to the environment in brief as the “bulge” and on smaller scales, the “halo”.

Results. We find simple descriptions of the simulations of collisionless matter by comparing predicted densities, velocity dispersions and distribution functions with the simulations. In some cases central point masses may be included by iteration. We emphasize that the co-eval self-similar growth allows an explanation of the black hole bulge mass correlation between approximately similar collisionless systems.

Conclusions. We have derived our results from first principles assuming adiabatic self-similarity and either self-similar virialisation or normal steady virialisation. We conclude that distribution functions that retain a memory of self-similar evolution provide an understanding of collisionless systems. The implied energy relaxation of the collisionless matter is due to the time dependence. Phase mixing relaxation may be enhanced by clump-clump interactions.