Chandra Observation of Abell 1142: A Cool-Core Cluster Lacking a Central
  Brightest Cluster Galaxy?
  Abell~1142 is a low-mass galaxy cluster at low redshift containing two
comparable Brightest Cluster Galaxies (BCG) resembling a scaled-down version of
the Coma Cluster. Our Chandra analysis reveals an X-ray emission peak, roughly
100 kpc away from either BCG, which we identify as the cluster center. The
emission center manifests itself as a second beta-model surface brightness
component distinct from that of the cluster on larger scales. The center is
also substantially cooler and more metal rich than the surrounding intracluster
medium (ICM), which makes Abell 1142 appear to be a cool core cluster. The
redshift distribution of its member galaxies indicates that Abell 1142 may
contain two subclusters with each containing one BCG. The BCGs are merging at a
relative velocity of ~1200 km/s. This ongoing merger may have shock-heated the
ICM from ~ 2 keV to above 3 keV, which would explain the anomalous L_X--T_X
scaling relation for this system. This merger may have displaced the
metal-enriched "cool core" of either of the subclusters from the BCG. The
southern BCG consists of three individual galaxies residing within a radius of
5 kpc in projection. These galaxies should rapidly sink into the subcluster
center due to the dynamical friction of a cuspy cold dark matter halo.
