Cosmological Simulations of Satellites around Isolated Dwarf Galaxies

Abstract

We trace the cosmological origin of satellites around a dwarf galaxy using a very high resolution (12~pc/h) cosmological hydrodynamic zoom simulation. To realistically describe the formation and evolution of small-mass stellar satellites, our model includes a full baryonic physics treatment including a recipe for UV self-shielding. We find that the mini-halos form objects resembling dwarf galaxies. Despite our high resolution, none of our 'mini-halos' form objects that might be considered globular cluster-like. Instead such objects are formed in the host galaxy's gaseous disk. We investigate why some form stars more efficiently than others. We find that the majority of their star forming gas is accreted after reionisation, thus the survival of a mini-halo's gas to reionisation is not an important factor. Instead, the key factor seems to be the ability for a mini-halo to cool its recently accreted gas, which is more efficient in more massive halos. We find halos in denser environments suffer more mergers, enabling them to grow their mass such that cooling of accreted gas can occur efficiently. Although the host galaxy is only a dwarf galaxy itself, we find that ram pressure is an efficient means by which accreted mini-halos lose their gas content, both by interacting with hot halo gas but also in direct collisions with the gas disk of the host. The satellites are also disrupted by the tidal forces near the center of the host galaxy. Compared to the disrupted satellites, surviving satellites are relatively more massive, but tend to infall later into the host galaxy, thus reducing the time they are subjected to destructive environmental mechanisms and dynamical friction. In summary, our results suggest that the characteristics of satellites are mainly determined by their ability to efficiently cool gas that is accreted in the redshift range z=3-5, prior to their infall into the host galaxy.