Speaker
Description
The Milky Way (MW) galaxy presents a larger number of satellites within 40 kpc than predicted by cosmological simulations of MW halos. If we believe simulation results, one implication is that halos as small as Vpeak~7 km/s should harbour galaxies, which is in contrast to the expectations of most galaxy formation models. On the other hand, idealized simulations predict that the cuspy NFW density profile of cold dark matter halos never fully disrupts, and show that cosmological N-body simulations suffer from artificial disruption of subhalos near the centers of MW-mass halos after tidal stripping. This is a numerical limitation due to the finite mass resolution currently achievable in these simulations.
In this work we use the Aquarius simulations of MW-mass halos, combined with the Galform semi-analytical galaxy formation model, to account for these sub-resolution subhalos (commonly known as “type-2s/orphans”) and estimate the true radial distribution of satellite galaxies predicted by LCDM. We carry out a convergence study of the number of type-2s versus surviving satellites by comparing 5 different resolution levels and we characterize the population of type-2s. Our results show that the observed population of nearby ultrafaint MW satellites can be readily accommodated within LCDM models where galaxy formation occurs in halos with masses above the Hydrogen-cooling limit.
