Journal Club: 20/02/2009

We continue our series on how baryons contribute to dark matter halo formation with this tasty morsel: http://arxiv.org/abs/0902.2100.

We analyse the dark matter (DM) distribution in a approx 10^12 M_sun halo extracted from a simulation consistent with the concordance cosmology, where the physics regulating the transformation of gas into stars was allowed to change producing galaxies with different morphologies. Although the DM profiles get more concentrated as baryons are collected at the centre of the haloes compared to a pure dynamical run, the total baryonic mass alone is not enough to fully predict the reaction of the DM profile. We also note that baryons affect the DM distribution even outside the central regions. Those systems where the transformation of gas into stars is regulated by Supernova (SN) feedback, so that significant disc structures are able to form, are found to have more concentrated dark matter profiles than a galaxy which has efficiently transformed most of its baryons into stars at early times. The accretion of satellites is found to be associated with an expansion of the dark matter profiles, triggered by angular momentum transfer from the incoming satellites. As the impact of SN feedback increases, the satellites get less massive and are even strongly disrupted before getting close to the main structure causing less angular momentum transfer. Our findings suggest that the response of the DM halo is driven by the history of assembly of baryons into a galaxy along their merger tree.