Dark matter-radiation interactions: the structure of Milky Way satellite galaxies

TL;DR

This paper investigates how dark matter-radiation interactions influence the formation and properties of Milky Way satellite galaxies, showing that such interactions can reduce subhalo concentration and align simulations with observations.

Contribution

It demonstrates through high-resolution simulations that dark matter-radiation interactions can resolve the 'too big to fail' problem by altering subhalo dynamics.

Findings

Reduced concentration of large subhaloes with interactions

Rotation curves match observational data

Fewer small-scale subhaloes due to suppressed power spectrum

Abstract

In the thermal dark matter (DM) paradigm, primordial interactions between DM and Standard Model particles are responsible for the observed DM relic density. In Boehm et al. (2014), we showed that weak-strength interactions between DM and radiation (photons or neutrinos) can erase small-scale density fluctuations, leading to a suppression of the matter power spectrum compared to the collisionless cold DM (CDM) model. This results in fewer DM subhaloes within Milky Way-like DM haloes, implying a reduction in the abundance of satellite galaxies. Here we use very high resolution N-body simulations to measure the dynamics of these subhaloes. We find that when interactions are included, the largest subhaloes are less concentrated than their counterparts in the collisionless CDM model and have rotation curves that match observational data, providing a new solution to the "too big to fail" problem.