Cosmological particle-based simulations of galaxy formation; numerical loss of angular momentum and disk heating

We discuss the role that numerical effects have in cosmological N-Body/SPH simulations of disk galaxy formation. We show that the resolution of current state-of-the-art calculations, about $10^5$ SPH and dark matter particles within the virial radius of a Milky Way-sized halo at $z=0$, is just enough to avoid artificial losses of angular momentum and dramatic numerical disk heating during the phase of disk assembly. Instead both effects will still be an issue at earlier epochs, when the progenitors of the final galaxies are resolved by significantly less than $10^5$ particles.This must be at least partially responsible for why simulations show a ubiquitous low angular momentum spheroid that is too massive compared to that of typical disk galaxies