The influence of baryonic cooling on the halo-configuration of the dark matter
From November 2005 to July 2007 I worked on my master thesis (german: Diplomarbeit) at the Leibniz-Institute for Astrophysics Potsdam (AIP). The aim was to investigate a halo of dark matter and baryonic gas and to analyse the dynamics of the system in consequence of the gas contraction due to cooling. This was done in a spherically symmetic halo.
We treated the dark matter and the gas as a two-fluid system. This can be done assuming local Maxwellian velocity distribution for the dark matter at any time. If any re-distribution of the dark matter particles comes along with violent relaxation processes having short characteristic times and the distribution is sufficiently coarse-grained, this assumption is a good approximation.
The considered model consists then of two independent fluids coupled by the gravitational potential only. The initial conditions were realized by a stationary polytropic sphere for the gas component. For the dark matter component the stationary Jeans equation for a given density distribution is solved. The dynamics were computed by an Eulerian first-order Godunov-type code, which I developed based on a code by E. Toro.
In this simple model, a halo of the size and mass comparable to that of a galaxy collapses completely when the gas is cooled. The presence of dark matter accelerates the collapse considerably. In case of a halo with a mass of about 100000 solar masses the behavior depends strongly on the initial density profile and therefore on the temperature. The halo is either collapsing or reaches a quasi-stationary state. The time evolution shows a specific behavior.
The full text of my thesis can be found here. Unfortunately it is written in german.
In July 2008 we published the main results in Klar & Mücket 2008.