Observable tests of self-interacting dark matter in galaxy clusters: BCG wobbles in a constant density core. (arXiv:1812.06981v1 [astro-ph.CO])
<a href="http://arxiv.org/find/astro-ph/1/au:+Harvey_D/0/1/0/all/0/1">David Harvey</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Robertson_A/0/1/0/all/0/1">Andrew Robertson</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Massey_R/0/1/0/all/0/1">Richard Massey</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+McCarthy_I/0/1/0/all/0/1">Ian G. McCarthy</a>
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.
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.
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