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

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