Models of Cold Dark Matter predict that the distribution of dark matter in galaxy clusters should be cuspy, centrally concentrated. Constant density cores would be strong evidence for beyond-CDM physics, such as Self-Interacting Dark Matter (SIDM). An observable consequence would be oscillations of the Brightest Cluster Galaxy (BCG) in otherwise relaxed galaxy clusters. Offset BCGs have indeed been observed - but only interpreted via a simplified, analytic model of oscillations. We compare these observations to the BAHAMAS-SIDM suite of cosmological simulations, which include SIDM and a fully hydrodynamical treatment of star formation and feedback. We predict that the median offset of BCGs increases with the SIDM cross-section, cluster mass and the amount of stellar mass within 10kpc, while CDM exhibits no trend in mass. Interpolating between the simulated cross-sections, we find that the observations (of 10 clusters) is consistent with CDM at the ~1.5σ level, and prefer cross-section σ/m < 0.12(0.39)cm2/g at 68% (95%) confidence level. This is on the verge of ruling out velocity-independent dark matter self-interactions as the solution to discrepancies between the predicted and observed behaviour of dwarf galaxies, and will be improved by larger surveys by Euclid or SuperBIT.
@article{arxiv.1812.06981,
title = {Observable tests of self-interacting dark matter in galaxy clusters: BCG wobbles in a constant density core},
author = {David Harvey and Andrew Robertson and Richard Massey and Ian G. McCarthy},
journal= {arXiv preprint arXiv:1812.06981},
year = {2019}
}