ore-collapse, evaporation and tidal effects: the life story of a self-interacting dark matter subhalo

Self-interacting dark matter (SIDM) cosmologies admit an enormous diversityof dark matter (DM) halo density profiles, from low-density cores tohigh-density core-collapsed cusps. The possibility of the growth of highcentral density in low-mass halos, accelerated if halos are subhalos of largersystems, has intriguing consequences for small-halo searches with substructurelensing. However, following the evolution of $\lesssim 10^8 M_\odot$ subhalosin lens-mass systems ($\sim 10^{13}M_\odot$) is computationally expensive withtraditional N-body simulations. In this work, we develop a new hybridsemi-analytical + N-body method to study the evolution of SIDM subhalos withhigh fidelity, from core formation to core-collapse, in staged simulations. Ourmethod works best for small subhalos ($\lesssim 1/1000$ host mass), for whichthe error caused by dynamical friction is minimal. We are able to capture theevaporation of subhalo particles by interactions with host halo particles, aneffect that has not yet been fully explored in the context of subhalocore-collapse. We find three main processes drive subhalo evolution: subhalointernal heat outflow, host-subhalo evaporation, and tidal effects. The subhalocentral density grows only when the heat outflow outweighs the energy gain fromevaporation and tidal heating. Thus, evaporation delays or even disruptssubhalo core-collapse. We map out the parameter space for subhalos tocore-collapse, finding that it is nearly impossible to drive core-collapse insubhalos in SIDM models with constant cross sections. Any discovery ofultra-compact dark substructures with future substructure lensing observationsfavors additional degrees of freedom, such as velocity-dependence, in the crosssection.