Witnessing the Formation of a Brightest Cluster Galaxy in a Nearby X-ray
  Cluster
  The central dominant galaxies in galaxy clusters constitute the most massive
and luminous galaxies in the Universe. Despite this, the formation of these
brightest cluster galaxies (BCGs) and the impact of this on the surrounding
cluster environment remain poorly understood. Here we present multi-wavelength
observations of the nearby poor X-ray cluster MZ 10451, in which both processes
can be studied in unprecedented detail. Chandra observations of the
intracluster medium (ICM) in the cluster core, which harbors two optically
bright early-type galaxies in the process of merging, show that the system has
retained a cool core and a central metal excess. This suggests that any
merger-induced ICM heating and mixing remain modest at this stage. Tidally
stripped stars seen around either galaxy likely represent an emerging
intracluster light component, and the central ICM abundance enhancement may
have a prominent contribution from in situ enrichment provided by these stars.
The smaller of the merging galaxies shows evidence for having retained a hot
gas halo, along with tentative evidence for some obscured star formation,
suggesting that not all BCG major mergers at low redshift are completely
dissipationless. Both galaxies are slightly offset from the peak of the ICM
emission, with all three lying on an axis that roughly coincides with the
large-scale elongation of the ICM. Our data are consistent with a picture in
which central BCGs are built up by mergers close to the cluster core, by
galaxies infalling on radial orbits aligned with the cosmological filaments
feeding the cluster.
