# Observable tests of self-interacting dark matter in galaxy clusters: BCG wobbles in a constant density core

Harvey, D, Robertson, A, Massey, R and McCarthy, IG (2019) Observable tests of self-interacting dark matter in galaxy clusters: BCG wobbles in a constant density core. Monthly Notices of the Royal Astronomical Society, 488 (2). pp. 1572-1579. ISSN 0035-8711

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Observable tests of self-interacting dark matter in galaxy clusters BCG wobbles in a constant density core.pdf - Published Version

Models of Cold Dark Matter always predict a cuspy, centrally concentrated distribution of dark matter in galaxy clusters. 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 and cluster mass, while CDM exhibits no trend in mass. Interpolating between the simulated cross-sections, we find that the observations (of 10 clusters) have a 38% probability of being consistent with CDM, and prefer cross-section $\sigma/m < 0.22$cm$^2$/g at 95% confidence level. This is on the verge of discriminating between dark matter models that would explain discrepancies in the behaviour of dwarf galaxies, and will be improved by larger surveys by Euclid or SuperBIT.