Satellite survival in highly resolved Milky Way class haloes

Surprisingly little is known about the origin and evolution of the Milky Way's satellite galaxy companions. Ultraviolet (UV) photoionization, supernova feedback and interactions with the larger host halo are all thought to play a role in shaping the population of satellites that we observe today, but there is still no consensus as to which of these effects, if any, dominates. In this paper, we revisit the issue by re-simulating a Milky Way class dark matter halo with unprecedented resolution. Our set of cosmological hydrodynamic adaptive mesh refinement simulations, called the NUT suite, allows us to investigate the effect of supernova feedback and UV photoionization at high redshift with subparsec resolution. We subsequently follow the effect of interactions with the Milky-Way-like halo using a lower spatial resolution (50 pc) version of the simulation down to z = 0. This latter produces a population of simulated satellites that we compare to the observed satellites of the Milky Way and M31. We find that supernova feedback reduces star formation in the least massive satellites but enhances it in the more massive ones. Photoionization appears to play a very minor role in suppressing star and galaxy formation in all progenitors of satellite haloes. By far the largest effect on the satellite population is found to be the mass of the host and whether gas cooling is included in the simulation or not. Indeed, inclusion of gas cooling dramatically reduces the number of satellites captured at high redshift which survive down to z = 0.