Are dark matter halos described by the fermionic King model?
Résumé
We consider the possibility that dark matter halos are made of massive neutrinos (e.g., sterile neutrinos) described by the fermionic King model. This model takes into account the Pauli exclusion principle and the escape of high energy particles. It has a finite mass. Dwarf halos are in a quantum (degenerate) condensed phase. Intermediate size halos are partially degenerate. Large halos are in a classical (nondegenerate) gaseous phase. Because of collisions and evaporation their central density increases until the gravothermal catastrophe sets in. The marginal King profile can be approximated by the modified Hubble profile which is similar to the Burkert profile that provides a good fit of dark matter halos. Some halos may undergo core collapse. For large halos, this leads to the formation of a central black hole. For small halos, the collapse is stopped by quantum degeneracy. This leads to a condensed object and to the expulsion of a massive atmosphere. We argue that large dark matter halos should not contain fermion balls because these nucleus-halo structures are saddle points of entropy.