Feedback, scatter and structure in the core of the PKS 0745-191 galaxy
  cluster
  We present Chandra X-ray Observatory observations of the core of the galaxy
cluster PKS 0745-191. Its centre shows X-ray cavities caused by AGN feedback
and cold fronts with an associated spiral structure. The cavity energetics
imply they are powerful enough to compensate for cooling. Despite the evidence
for AGN feedback, the Chandra and XMM-RGS X-ray spectra are consistent with a
few hundred solar masses per year cooling out of the X-ray phase, sufficient to
power the emission line nebula. The coolest X-ray emitting gas and brightest
nebula emission is offset by around 5 kpc from the radio and X-ray nucleus.
Although the cluster has a regular appearance, its core shows density,
temperature and pressure deviations over the inner 100 kpc, likely associated
with the cold fronts. After correcting for ellipticity and projection effects,
we estimate density fluctuations of ~4 per cent, while temperature, pressure
and entropy have variations of 10-12 per cent. We describe a new code, MBPROJ,
able to accurately obtain thermodynamical cluster profiles, under the
assumptions of hydrostatic equilibrium and spherical symmetry. The
forward-fitting code compares model to observed profiles using Markov Chain
Monte Carlo and is applicable to surveys, operating on 1000 or fewer counts. In
PKS0745 a very low gravitational acceleration is preferred within 40 kpc radius
from the core, indicating a lack of hydrostatic equilibrium, deviations from
spherical symmetry or non-thermal sources of pressure.
