Oral Presentation

Hierarchical formation of dark matter halos near the free streaming scale and implications for annihilation signals

Author(s): Tomoaki Ishiyama (Chiba University)

Presenter: Tomoaki Ishiyama (Chiba University)

The free streaming motion of dark matter particles imprints a cutoff in the matter power spectrum and set the scale of the smallest dark matter halo. Recent cosmological N-body simulations have shown that the central density cusp is much steeper in halos near the free streaming scale than in more massive halos. Here, we study the abundance and structure of subhalos near the free streaming scale using a suite of unprecedentedly large cosmological N-body simulations, over a wide range of the host halo mass. The subhalo abundance is suppressed strongly below the free streaming scale, but the ratio between the subhalo mass function in the cutoff and no cutoff simulations is well fitted by a single correction function regardless of the host halo mass and the redshift. In subhalos, the central density cusp is considerably shallower than in field halos, however, is still steeper than that of the NFW profile. The concentrations are significantly larger in subhalos than halos and depend on the subhalo mass.