Modelling self-interacting dark matter substructures I: Calibration with N-body simulations of a Milky-Way-sized halo and its satellite

TL;DR

This study uses N-body simulations and a semi-analytic model to investigate the evolution of self-interacting dark matter subhaloes in a Milky-Way-sized galaxy, focusing on tidal effects and core stability over 10 Gyr.

Contribution

It calibrates a gravothermal fluid model for SIDM subhaloes and develops a semi-analytic framework incorporating tidal stripping and self-scattering effects.

Findings

Tidal effects in SIDM subhaloes can be modeled similarly to CDM but with faster mass loss.

No prominent gravothermal collapse observed for cross sections below 10 cm^2/g over 10 Gyr.

Semi-analytic model effectively predicts SIDM subhalo evolution, pending improvements for baryonic effects.

Abstract

We study evolution of single subhaloes with their masses of $\sim10^9 M_\odot$ in a Milky-Way-sized host halo for self-interacting dark matter (SIDM) models. We perform dark-matter-only N-body simulations of dynamical evolution of individual subhaloes orbiting its host by varying self-scattering cross sections (including a velocity-dependent scenario), subhalo orbits, and internal properties of the subhalo. We calibrate a gravothermal fluid model to predict time evolution in spherical mass density profiles of isolated SIDM haloes with the simulations. We find that tidal effects of SIDM subhaloes can be described with a framework developed for the case of collision-less cold dark matter (CDM), but a shorter typical time scale for the mass loss due to tidal stripping is required to explain our SIDM simulation results. As long as the cross section is less than $\sim10\, \mathrm{cm}^2/\mathrm{g}$ and initial states of subhaloes are set within a $2\sigma$-level scatter at redshifts of $\sim2$ predicted by the standard $\Lambda$CDM cosmology, our simulations do not exhibit a prominent feature of gravothermal collapse in the subhalo central density for 10 Gyr. We develop a semi-analytic model of SIDM subhaloes in a time-evolving density core of the host with tidal stripping and self-scattering ram pressure effects. Our semi-analytic approach provides a simple, efficient and physically-intuitive prediction of SIDM subhaloes, but further improvements are needed to account for baryonic effects in the host and the gravothermal instability accelerated by tidal stripping effects.