Escalating core formation with dark matter self-heating

Abstract

Exothermic scatterings of dark matter (DM) produce DM particles with significant kick velocities inside DM halos. In collaboration with DM self-interaction, the excess kinetic energy of the produced DM particles is distributed to the others, which self-heats the DM particles as a whole. The DM self-heating is efficient towards the halo center, and the heat injection is used to enhance the formation of a uniform density core inside halos. The effect of DM self-heating is expected to be more significant in smaller halos for two reasons: 1) the exothermic cross section times the relative velocity, $⟨{\ensuremath{\sigma}}_{\mathrm{exo}}{v}_{\mathrm{rel}}⟩$, is constant; 2) and the ratio of the injected heat to the velocity dispersion squared gets larger toward smaller-size halos. For the first time, we quantitatively investigate the core formation from DM self-heating for halos in a wide mass range (${10}^{9}--{10}^{15}\text{ }\text{ }{\mathrm{M}}_{\ensuremath{\bigodot}}$) using the gravothermal fluid formalism. Notably, we demonstrate that the core formation is sharply escalating toward smaller-size halos by taking the self-heating DM (i.e., DM that semiannihilates and self-interacts) as an example. We show that the sharp escalation of the core formation may cause a tension in simultaneously explaining the observed central mass deficit of Milky Way satellites and field dwarf/low surface brightness spiral galaxies. We expect DM self-heating to be present also in other models that exhibit exothermic scatterings and self-interaction of DM, which can appreciably contribute to the core formation of DM halos.