Baryonic impact on the dark matter distribution in Milky Way-sized galaxies and their satellites

We study the impact of baryons on the distribution of dark matter in a Milky Way-sized halo by comparing a high-resolution, moving mesh cosmological simulation with its dark matter-only counterpart. We identify three main processes related to baryons - adiabatic contraction, tidal disruption, and reionization - which jointly shape the dark matter distribution in both the main halo and its subhaloes. The relative effect of each baryonic process depends strongly on the subhalo mass. For massive subhaloes with maximum circular velocity v(max) > 35 km s(-1), adiabatic contraction increases the dark matter concentration, making these haloes less susceptible to tidal disruption. For low-mass subhaloes with v(max) < 20 km s(-1), reionization effectively reduces their mass on average by a parts per thousand 30 per cent and v(max) by a parts per thousand 20 per cent. For intermediate subhaloes with 20 km s(-1) < v(max) < 35 km s(-1), which share a similar mass range as the classical dwarf spheroidals, strong tidal truncation induced by the main galaxy reduces their v(max). As a combined result of reionization and increased tidal disruption, the total number of low-mass subhaloes in the hydrodynamic simulation is nearly halved compared to that of the N-body simulation. We do not find dark matter cores in dwarf galaxies, unlike previous studies that employed bursty feedback-driven outflows. The substantial impact of baryons on the abundance and internal structure of subhaloes suggests that galaxy formation and evolution models based on N-body simulations should include these physical processes as major components.