  Galaxy clusters' structure, dominated by dark matter, is traced by member
galaxies in the optical and hot intra-cluster medium (ICM) in X-rays. We
compare the radial distribution of these components and determine the
mass-to-light ratio vs. system mass relation.
  We use 14 clusters from the REXCESS sample which is representative of
clusters detected in X-ray surveys. Photometric observations with the Wide
Field Imager on the 2.2m MPG/ESO telescope are used to determine the number
density profiles of the galaxy distribution out to $r_{200}$. These are
compared to electron density profiles of the ICM obtained using XMM-Newton, and
dark matter profiles inferred from scaling relations and an NFW model.
  While red sequence galaxies trace the total matter profile, the blue galaxy
distribution is much shallower. We see a deficit of faint galaxies in the
central regions of massive and regular clusters, and strong suppression of
bright and faint blue galaxies in the centres of cool-core clusters,
attributable to ram pressure stripping of gas from blue galaxies in high
density regions of ICM and disruption of faint galaxies due to galaxy
interactions. We find a mass-to-light ratio vs. mass relation within $r_{200}$
of $\left(3.0\pm0.4\right) \times 10^2\,
h\,\mathrm{M}_{\odot}\,\mathrm{L}_{\odot}^{-1}$ at
$10^{15}\,\mathrm{M}_{\odot}$ with slope $0.16 \pm 0.14$, consistent with most
previous results.
