Abstract
We use the "Evolution and assembly of galaxies and their environment" (EAGLE)
cosmological simulation to investigate the effect of baryons on the density
profiles of rich galaxy clusters. We focus on the six most massive EAGLE
clusters ($M_200 > 10^14M_ødot$) which can be compared with a recent
analysis of seven real clusters by Newman et al. The central brightest cluster
galaxies (BCGs) in EAGLE have steep stellar density profiles, $\rho_*(r)
r^-3$. Stars dominate the mass density for $r < 10~kpc$, and,
as a result, the total mass density profiles are steeper than the
Navarro-Frenk-White (NFW) profile. However, the dark matter halo itself closely
follows the NFW form at all resolved radii ($r\gtrsim3.0~kpc$). The
BCGs have similar surface brightness and line-of-sight velocity
dispersion profiles as the BCGs observed by Newmanet al. The central slopes of
the total mass profiles are also consistent with the observed clusters.
However, after subtracting the contribution of the stars to the central
density, Newman et al. find significantly shallower slopes than NFW, in
contradiction with the EAGLE results. We discuss possible reasons for this
discrepancy, such as differences in the mass of the simulated and observed
clusters or orientation biases in the observed sample. We conclude that an
inconsistency between the kinematical model adopted by Newman et al. for their
BCGs, which assumes isotropic stellar orbits, and the kinematical structure of
the EAGLE BCGs, in which the orbital stellar anisotropy varies with radius and
tends to be radially biased, could explain at least part of the discrepancy.
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