Kavli Affiliate: Michael McDonald
| First 5 Authors: Cian Roche, Michael McDonald, Josh Borrow, Mark Vogelsberger, Xuejian Shen
| Summary:
The distribution of offsets between the brightest cluster galaxies of galaxy
clusters and the centroid of their dark matter distributions is a promising
probe of the underlying dark matter physics. In particular, since this
distribution is sensitive to the shape of the potential in galaxy cluster
cores, it constitutes a test of dark matter self-interaction on the largest
mass scales in the universe. We examine these offsets in three suites of modern
cosmological simulations; IllustrisTNG, MillenniumTNG and BAHAMAS. For clusters
above $10^{14}rm{M_odot}$, we examine the dependence of the offset
distribution on gravitational softening length, the method used to identify
centroids, redshift, mass, baryonic physics, and establish the stability of our
results with respect to various nuisance parameter choices. We find that
offsets are overwhelmingly measured to be smaller than the minimum converged
length scale in each simulation, with a median offset of $sim 1rm{kpc}$ in
the highest resolution simulation considered, TNG300-1, which uses a
gravitational softening length of $1.48rm{kpc}$. We also find that centroids
identified via source extraction on smoothed dark matter and stellar particle
data are consistent with the potential minimum, but that observationally
relevant methods sensitive to cluster strong gravitational lensing scales, or
those using the the "light traces mass" approach, in this context meaning gas
is used as a tracer for the potential, can overestimate offsets by factors of
$sim10$ and $sim30$, respectively. This has the potential to reduce tensions
with existing offset measurements which have served as evidence for a nonzero
dark matter self-interaction cross section.
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