Self-Interacting Dark Matter and Small-Scale Gravitational Lenses in Galaxy Clusters

TL;DR

This paper investigates how self-interacting dark matter (SIDM) can explain the excess of small-scale gravitational lenses observed in galaxy clusters, contrasting it with standard cold dark matter (CDM) through simulations.

Contribution

It introduces controlled N-body simulations incorporating observational constraints to compare SIDM and CDM effects on gravitational lensing in galaxy clusters.

Findings

SIDM can produce steeper density profiles than CDM.

SIDM may explain small-scale lensing excess in clusters.

High baryon concentration in substructures is necessary for lensing observations.

Abstract

Recently, Meneghetti et al. reported an excess of small-scale gravitational lenses in galaxy clusters. We study its implications for self-interacting dark matter (SIDM), compared with standard cold dark matter (CDM). We design controlled N-body simulations that incorporate observational constraints. The presence of early-type galaxies in cluster substructures can deepen gravitational potential and reduce tidal mass loss. Both scenarios require a relatively high baryon concentration in the substructure to accommodate the lensing measurements, and their tangential caustics are similar. The SIDM substructure can experience gravothermal collapse and produce a steeper density profile than its CDM counterpart, leading to a larger radial galaxy-galaxy strong lensing cross section, although this effect is hard to observe. Our results indicate SIDM can provide a unified explanation to small-scale lenses in galaxy clusters and stellar motions in dwarf galaxies.