Preprocessing, mass-loss and mass segregation of galaxies in dark matter simulations

We investigate the mass-loss of galaxies in groups and clusters with high-resolution dark matter simulations. We detect weak mass segregation in the inner regions of group/cluster haloes, consistent with observational findings. This applies to samples of galaxy analogues selected using either their present-day mass or past maximum (peak) mass. We find a strong radial trend in the fractional mass lost by the galaxies since peak, independent of their mass. This suggests that segregation is due to massive galaxies having formed closer to the halo centres and not the preferential destruction of smaller galaxies near halo centres. We divide our sample into galaxies that were accreted as a group versus as a single, distinct halo. We find strong evidence for preprocessing – the grouped galaxies lose ∼35–45 per cent of their peak mass before being accreted on to their final host haloes, compared to single galaxies that lose ∼12 per cent. After accretion, however, the single galaxies lose more mass compared to the grouped ones. These results are consistent with a scenario in which grouped galaxies are preprocessed in smaller haloes while single galaxies ‘catch up’ in terms of total mass-loss once they are accreted on to the final host halo. The fractional mass-loss is mostly independent of the galaxy mass and host mass, and increases with amount of time spent in a dense environment.