# The Milky Way's Halo and Subhalos in Self-Interacting Dark Matter

## TL;DR

This study uses high-resolution simulations to compare self-interacting dark matter and cold dark matter models of the Milky Way, revealing differences in halo density profiles and subhalo properties, especially when baryonic effects are included.

## Contribution

First detailed comparison of SIDM and CDM galaxy simulations with baryonic effects, highlighting differences in halo density and subhalo characteristics.

## Key findings

- SIDM host halo is denser in the center with no core when baryons are included.
- Massive subhalos in SIDM are less dense than in CDM at small radii.
- Baryonic potential mitigates the too-big-to-fail problem in both models.

## Abstract

We perform high-resolution simulations of a MW-like galaxy in a self-interacting cold dark matter model with elastic cross section over mass of $1~\rm cm^2/g$ (SIDM) and compare to a model without self-interactions (CDM). We run our simulations with and without a time-dependent embedded potential to capture effects of the baryonic disk and bulge contributions. The CDM and SIDM simulations with the embedded baryonic potential exhibit remarkably similar host halo profiles, subhalo abundances and radial distributions within the virial radius. The SIDM host halo is denser in the center than the CDM host and has no discernible core, in sharp contrast to the case without the baryonic potential (core size $\sim 7 \, \rm kpc$). The most massive subhalos (with $V_{\mathrm{peak}}> 20 \, \rm km/s$) in our SIDM simulations, expected to host the classical satellite galaxies, have density profiles that are less dense than their CDM analogs at radii less than 500 pc but the deviation diminishes for less massive subhalos. With the baryonic potential included in the CDM and SIDM simulations, the most massive subhalos do not display the too-big-to-fail problem. However, the least dense among the massive subhalos in both these simulations tend to have the smallest pericenter values, a trend that is not apparent among the bright MW satellite galaxies.