Erwin T. Lau, Daisuke Nagai, Andrey V. Kravtsov, Alexey Vikhlinin, Andrew R. Zentner
Simulations of cluster formation have demonstrated that condensation of
baryons into central galaxies during cluster formation can drive the shape of
the gas distribution in galaxy clusters significantly rounder, even at radii as
large as half of the virial radius. However, such simulations generally predict
stellar fractions within cluster virial radii that are ~2-3 times larger than
the stellar masses deduced from observations. In this work we compare
ellipticity profiles of clusters simulated with and without baryonic cooling to
the cluster ellipticity profiles derived from Chandra and ROSAT observations in
an effort to constrain the fraction of gas that cools and condenses into the
central galaxies within clusters. We find that the observed ellipticity
profiles are fairly constant with radius, with an average ellipticity of 0.18
+/- 0.05. The observed ellipticity profiles are in good agreement with the
predictions of non-radiative simulations. On the other hand, the ellipticity
profiles of the clusters in simulations that include radiative cooling, star
formation, and supernova feedback (but no AGN feedback) deviate significantly
from the observed ellipticity profiles at all radii. The non-radiative
simulations overpredict (underpredict) ellipticity in the inner (outer) regions
of galaxy clusters. By comparing the simulations with and without cooling, we
show that the cooling of gas via cooling flows in the central regions of
simulated clusters causes the gas distribution to be more oblate in the central
regions, but makes the outer gas distribution more spherical. We find that
late-time gas cooling and star formation is responsible for the significantly
oblate gas distributions in cluster cores, but the gas shapes outside of
cluster cores are set primarily by baryon dissipation at high-redshift z > 2.
View original:
http://arxiv.org/abs/1201.2168
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