Relaxation of dark matter halos: how to match observational data?

¹ DESY Zeuthen Platanenallee 6, 15738 Zeuthen, Germany
e-mail: baushev@gmail.com
² Institut für Physik und Astronomie, Universität Potsdam, 14476 Potsdam-Golm, Germany

Received: 23 September 2013
Accepted: 25 June 2014

Abstract

We show that moderate energy relaxation in the formation of dark matter halos invariably leads to profiles that match those observed in the central regions of galaxies. The density profile of the central region is universal and insensitive to either the seed perturbation shape or the details of the relaxation process. The profile has a central core; the multiplication of the central density by the core radius is almost independent of the halo mass, in accordance with observations. In the core area the density distribution behaves as an Einasto profile with low index (n ~ 0.5); it has an extensive region with ρ ∝ r^-2 at larger distances. This is exactly the shape that observations suggest for the central region of galaxies. On the other hand, this shape does not fit the galaxy cluster profiles. A possible explanation of this fact is that the relaxation is violent in the case of galaxy clusters; however, it is not violent enough when galaxies or smaller dark matter structures are considered. We discuss the reasons for this.