  We explore the near-infrared (NIR) $K$-band properties of galaxies within 93
galaxy clusters and groups using data from the 2MASS. We use X-ray properties
of these clusters to pinpoint cluster centers and estimate cluster masses. By
stacking all these systems, we study the shape of the cluster luminosity
function and the galaxy distribution within the clusters. We find that the
galaxy profile is well described by the NFW profile with a concentration
parameter c~3, with no evidence for cluster mass dependence of the
concentration. Using this sample, whose masses span the range from
$3\times10^{13}M_\odot$ to $2\times10^{15}M_\odot$, we confirm the existence of
a tight correlation between total galaxy NIR luminosity and cluster binding
mass, which indicates that NIR light can serve as a cluster mass indicator.
  From the observed galaxy profile, together with cluster mass profile
measurements from the literature, we find that the \mlr is a weakly decreasing
function of cluster radius, and that it increases with cluster mass. We also
derive the mean number of galaxies within halos of a given mass. We find that
the mean number scales as $N\propto M^{0.84\pm0.04}$ for galaxies brighter than
$M_K=-21$, indicating high mass clusters have fewer galaxies per unit mass than
low mass clusters. Using published observations at high redshift, we show that
higher redshift clusters have higher mean occupation number than nearby systems
of the same mass. By comparing the luminosity function & radial distribution of
galaxies in low mass and high mass clusters, we show that there is a marked
decrease in the number density of galaxies fainter than $M_*$ as one moves to
higher mass clusters; in addition, extremely luminous galaxies are more
probable in high mass clusters.
