Detection of a Superluminous Spiral Galaxy in the Heart of a Massive
  Galaxy Cluster
  It is well established that brightest cluster galaxies (BCGs), residing in
the center of galaxy clusters, are typically massive and quenched galaxies with
cD or elliptical morphology. An optical survey suggested that an exotic galaxy
population, superluminous spiral and lenticular galaxies could be the BCGs of
some galaxy clusters. Because the cluster membership and the centroid of a
cluster cannot be accurately determined based solely on optical data, we
followed up a sample of superluminous disk galaxies and their environment using
XMM-Newton X-ray observations. Specifically, we explored seven superluminous
spiral and lenticular galaxies that are candidate BCGs. We detected massive
galaxy clusters around five superluminous disk galaxies and established that
one superluminous spiral, 2MASX J16273931+3002239, is the central BCG of a
galaxy cluster. The temperature and total mass of the cluster are $kT_{\rm
500}=3.55^{+0.18}_{-0.20}$ keV and $M_{\rm 500} = (2.39 \pm 0.19) \times
10^{14} \ \rm{M_{\odot}} $. We identified the central galaxies of the four
clusters that do not host the superluminous disk galaxy at their cores and
established that the centrals are massive elliptical galaxies. However, for two
of the clusters, the offset superluminous spirals are brighter than the central
galaxies, implying that the superluminous disk galaxies are the brightest
cluster galaxies. Our results demonstrate that superluminous disk galaxies are
rarely the central systems of galaxy clusters. This is likely because galactic
disks are destroyed by major mergers, which are more frequent in high-density
environments. We speculate that the disks of superluminous disk galaxies in
cluster cores may have been re-formed due to mergers with a gas-rich satellite.
