Structure and Subhalo Population of Halos in a Self-interacting Dark Matter Cosmology

A series of high-resolution numerical simulations were performed to study the structure and substructure of Milky Way-sized (MW-sized) and cluster-sized halos in a ΛCDM cosmology with self-interacting (SI) dark matter particles. The cross section per unit of particle mass has the form σ_DM=σ₀(1/v₁₀₀)^α, where σ₀ is a constant in units of cm² g^-1 and v₁₀₀ is the relative velocity in units of 100 km s^-1. Different values for σ₀ with α=0 or 1 were used. For small values of σ_DM=const (<~0.5, α=0), the core density of the halos at z=0 is typically higher at a given mass for lower values of σ₀ or, at a given σ₀, for lower masses. For values of σ₀ as high as 3.0, both cluster- and MW-sized halos may undergo the gravothermal catastrophe before z=0. The core expansion occurs in a stable regime because the heat capacity C is positive in the center. After the maximum expansion, the isothermal core is hotter than the periphery and C<0. Then the gravothermal catastrophe is triggered. The instability onset can be delayed by both the dynamical heating of the halo by major mergers and the interaction of cool particles with the hot environment of a host halo. When α=1, the core density of cluster- and MW-sized halos is similar. Using σ_DM=0.5-1.0(1/v₁₀₀), our predictions agree with the central densities and the core scaling laws of halos inferred from the observations of both dwarf and low surface brightness galaxies and clusters of galaxies. Regarding the cumulative v_max function of subhalos within MW-sized halos, when (σ₀,α)=(0.1,0.0), (0.5, 0.0), or (0.5, 1.0) it agrees roughly with observations (luminous satellites) for v_max>~30 km s^-1, while at v_max=20 km s^-1 the functions are already a factor of 5-8 higher, similar to the CDM predictions. For (σ₀,α)=(1.0,1.0), this function lies above the corresponding CDM function. The structure and number of subhalos are affected by the scattering properties of the host halo rather than by those of the subhalos. The halos with SI have more specific angular momentum at a given mass shell and are rounder than their CDM counterparts. However, the angular momentum excess with regard to CDM is small. We conclude that the introduction of SI particles with σ_DM~1/v₁₀₀ may remedy the cuspy core problem of the CDM cosmogony, at the same time keeping a subhalo population similar to that of the CDM halos.