Detection of a Star Forming Galaxy in the Center of a Low-Mass Galaxy
  Cluster
  Brightest Cluster Galaxies (BCGs) residing in the centers of galaxy clusters
are typically quenched giant ellipticals. A recent study hinted that
star-forming galaxies with large disks, so-called superluminous spirals and
lenticulars, are the BCGs of a subset of galaxy clusters. Based on the existing
optical data it was not possible to constrain whether the superluminous disk
galaxies reside at the center of galaxy clusters. In this work, we utilize
XMM-Newton X-ray observations of five galaxy clusters to map the morphology of
the intracluster medium (ICM), characterize the galaxy clusters, determine the
position of the cluster center, and measure the offset between the cluster
center and the superluminous disk galaxies. We demonstrate that one
superluminous lenticular galaxy, 2MASX J10405643-0103584, resides at the center
of a low-mass ($M_{\rm 500} = 10^{14} \ \rm{M_{\odot}}$) galaxy cluster. This
represents the first conclusive evidence that a superluminous disk galaxy is
the central BCG of a galaxy cluster. We speculate that the progenitor of 2MASX
J10405643-0103584 was an elliptical galaxy, whose extended disk was re-formed
due to the merger of galaxies. We exclude the possibility that the other four
superluminous disk galaxies reside at the center of galaxy clusters, as their
projected distance from the cluster center is $150-1070$ kpc, which corresponds
to $(0.27-1.18)R_{\rm 500}$. We conclude that these clusters host quiescent
massive elliptical galaxies at their center.
