Role of prompt cusps in driving the core collapse of SIDM halos

TL;DR

This study uses high-resolution simulations to explore how prompt cusps influence the evolution and core collapse of isolated SIDM halos, revealing delayed evolution and complex interactions affecting collapse timing.

Contribution

It demonstrates the impact of prompt cusps on SIDM halo evolution, highlighting delayed core formation and nuanced effects on collapse driven by inner and outer halo interactions.

Findings

Halos with prominent PCs show delayed core formation by a factor of ~2.

During core collapse, halo evolution aligns in physical time after rescaling.

Deviations at late collapse are about 5%, influenced by concentration and outer halo velocity dispersion.

Abstract

Prompt cusps (PCs) form from the direct collapse of overdensities in the early Universe, reside at the center of every dark matter halo, and have density profiles steeper than $r^{-1}$ NFW cusps. Using a suite of high-resolution N-body simulations, we study the evolution of isolated halos in self-interacting dark matter (SIDM) with massive PCs embedded at their centers, a scenario that could be realized in certain SIDM models with light mediators that predict a small-scale suppression of the linear matter power spectrum. We track the evolution of three equally concentrated $10^7\,{\rm{M}}_\odot$ halos, hosting PCs of various total masses, and quantify how the presence of a PC affects the processes of core formation and collapse. Early in the core-formation phase, halos with more prominent PCs exhibit a delayed evolution by a factor of $\sim 2$ due to smaller velocity dispersion gradients in the inner region. During most of the core-collapse phase, the halo evolution becomes closely aligned in physical time, with appropriate rescaling of densities, radii, and velocity dispersions. The scale densities and radii preserve the virial mass of the original halos, but with increased concentration. Deviations occur at the late phase of core-collapse at the level of $\sim 5\%$ relative to the reference collapse track of an NFW halo. These deviations depend non-trivially on both the increased concentration incurred by the PCs, as well as the velocity dispersion (temperature) of the outer halo regions, which can inhibit or enhance the heat transfer process. Our simulations illustrate the complex interplay between the inner and outer halo profiles in determining the onset of core collapse and motivate future studies in the full cosmological context.