X-ray Substructure Studies of Four Galaxy Clusters using XMM-Newton Data
  Mahdavi et al. find that the degree of agreement between weak lensing and
X-ray mass measurements is a function of cluster radius. Numerical simulations
also point out that X-ray mass proxies do not work equally well at all radii.
The origin of the effect is thought to be associated with cluster mergers.
Recent work presenting the cluster maps showed an ability of X-ray maps to
reveal and study cluster mergers in detail. Here we present a first attempt to
use the study of substructure in assessing the systematics of the hydrostatic
mass measurements using two-dimensional (2-D) X-ray diagnostics. The
temperature map is uniquely able to identify the substructure in an almost
relaxed cluster which would be unnoticed in the ICM electron number density and
pressure maps. We describe the radial fluctuations in the 2-D maps by a
cumulative/differential scatter profile relative to the mean profile within/at
a given radius. The amplitude indicates ~10 fluctuations in the temperature,
electron number density and entropy maps, and ~15 fluctuations in the pressure
map. The amplitude of and the discontinuity in the scatter complement 2-D
substructure diagnostics, e.g. indicating the most disturbed radial range.
There is a tantalizing link between the substructure identified using the
scatter of the entropy and pressure fluctuations and the hydrostatic mass bias
relative to the expected mass based on the M-Yx and M-Mgas relations
particularly at r500. XMM-Newton observations with ~120,000 source photons from
the cluster are sufficient to apply our substructure diagnostics via the
spectrally measured 2-D temperature, electron number density, entropy and
pressure maps.
