Density Profile of Cool Core of Galaxy Clusters. (arXiv:1212.0671v1 [astro-ph.CO]):
The density profile of cool core of intracluster gas is investigated, for a
cluster of galaxies that is initially in the virial equilibrium state and then
undergoes radiative cooling. The initial gas profile is derived under the
assumption that the gas is hydrostatic within the dark matter potential
presented by so-called NFW or King model and has a polytropic profile. The
contribution from masses of gas and galaxies to the potential is ignored
compared to the dark matter in the calculation. The temperature and density
profiles of gas in its quasi-hydrostatic cooling phase, which is expected to
last for ~Gyr, is then calculated for different initial gas profiles. It is
found that in the quasi-hydrostatic cooling phase, while the temperature
decreases to be about one-third, the density increases by a factor of 4-6 at
the cluster center in comparison with their initial polytropic values, though
the profiles over the core depend on the dark matter potential. Hence, the core
radius in the quasi hydrostatic cooling gas appears smaller than the initial
polytropic one. We compare the density profile of the cool core with
observations to find that while the initial density is around the upper bounds
of large-core (>100 kpc) clusters, likely most relaxed but cooling is not yet
significant, the central density under quasi-hydrostatic cooling falls between
the mid- and high-values of small-core (<100 kpc) or cool-core clusters. It is
also found for the quasi-hydrostatic cooling gas that the entropy profile
roughly agrees with the best-fit model for the ACCEPT cluster sample with a low
central entropy, and the pressure gradient in the inner core is close to that
of the REXCESS sample. X-ray surface brightness calculated for the
quasi-hydrostatic cooling gas is well represented by the conventional double
beta-model, giving a physical basis of applying the double beta-model to cool
core clusters.
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