Uncovering substructure with wavelets: proof of concept using Abell 2744
  A recent comparison of the massive galaxy cluster Abell 2744 with the
Millennium XXL (MXXL) N-body simulation has hinted at a tension between the
observed substructure distribution and the predictions of LambdaCDM. Follow-up
investigations indicated that this could be due to the contribution from the
host halo and the subhalo finding algorithm used. To be independent of any
subhalo finding algorithm, we therefore investigate the particle data of the
MXXL simulation directly. We propose a new method to find substructures in 2D
mass maps using a wavelet transform, which treats the simulation and
observations equally. Using the same criteria to define a subhalo in
observations and simulated data, we find three Abell 2744 analogues in the MXXL
simulation. Thus the observations in Abell 2744 are in agreement with the
predictions of LambdaCDM. We investigate the reasons for the discrepancy
between the results obtained from the SUBFIND and full particle data analyses.
We find that this is due to incompatible substructure definitions in
observations and SUBFIND.
