Within the cosmological concordance model, Cold Dark Matter (CDM) subhalos form the building blocks which merge hierarchically to more massive galaxies. This concept requires that even nowadays massive galaxies are surrounded by numerous subhalos. Since intergalactic gas is accreted by massive galaxies, observable e.g. as high-velocity clouds (HVCs) around the Milky Way, with extremely low metallicities, these can be suggested to represent the baryonic content of primordial Dark Matter (DM) subhalos. Another possibility of their origin is that they stem from disrupted satellite galaxies, but in this case, these gas clouds move unaccompanied by a bound DM structure.

We simulate the evolution and survival of HVCs in both scenarios to distinguish between DM-dominated and DM-free clouds and to allow conclusions on their origin.

Part of this study was funded by the project no. HE1487/36 (S.P.) within the DFG Priority Program "Witnesses of Cosmic History: Formation and evolution of galaxies, their central black holes, and their environment".

Figure 1:

Simulation of a HVC with an initial mass of 4.4x10⁵ M_☉ after a time of 100 million years. The top left figure shows the evolution of a pure gas cloud, while the other panels demonstrate the appearance of HVCs which are embedded in different dark matter halos (clockwise: NFW halo, massive Burkert halo, low-mass Burkert halo). Color coded is the pressure with overlaid contour lines which indicate the integrated column density. The red contour line encloses the bound material. For more information see Ploeckinger & Hensler (2012, A&A, accepted).