Galaxy cluster luminosities and colours, and their dependence on cluster
  mass and merger state
  We study a sample of 19 galaxy clusters in the redshift range $0.15<z<0.30$
with highly complete spectroscopic membership catalogues (to $K < K^{\ast}(\rm
z)+1.5$) from the Arizona Cluster Redshift Survey (ACReS); individual
weak-lensing masses and near-infrared data from the Local Cluster Substructure
Survey (LoCuSS); and optical photometry from the Sloan Digital Sky Survey
(SDSS). We fit the scaling relations between total cluster luminosity in each
of six bandpasses (${\it grizJK}$) and cluster mass, finding cluster luminosity
to be a promising mass proxy with low intrinsic scatter $\sigma_{\ln L|M}$ of
only $\sim 10-20$ per cent for all relations. At fixed overdensity radius, the
intercept increases with wavelength, consistent with an old stellar population.
The scatter and slope are consistent across all wavelengths, suggesting that
cluster colour is not a function of mass. Comparing colour with indicators of
the level of disturbance in the cluster, we find a narrower variety in the
cluster colours of 'disturbed' clusters than of 'undisturbed' clusters. This
trend is more pronounced with indicators sensitive to the initial stages of a
cluster merger, e.g. the Dressler Schectman statistic. We interpret this as
possible evidence that the total cluster star formation rate is 'standardised'
in mergers, perhaps through a process such as a system-wide shock in the
intracluster medium.
