3. Initial conditions
The code follows the dynamical formation of galaxies since the moment in which the protohalo detaches itself from the Hubble flow with its cosmological share of baryonic material. Thus, we set ad hoc initial configuration for a protogalaxy and let the system evolve within the SPH scheme described above. Moreover, we assume that the star formation starts after the dark halo is virialized.
This approach is justified on the grounds that in this paper, we aimed to 1) test a simple but reasonable initial conditions set-up and 2) focus on processes which occur mainly at scales much smaller than the halo virial radius.
The working scenario is that, after a violent relaxation process which follows the separation from the Hubble expansion, the DM halo acquires a particular density distribution, and then accretes baryonic material which heats up to the halo virial temperature. Gas then radiatively cools and collapses, and through fragmentation, turns into the stars we see today in disks and spheroidal systems.
This scenario is not incompatible with the merging one, withstanding that the baryonic collapse takes place after the last merging episode.
© European Southern Observatory (ESO) 2000
Online publication: July 27, 2000