The Mysterious Merger of NGC6868 and NGC6861 in the Telescopium Group
  We use Chandra X-ray observations of the hot gas in and around NGC6868 and
NGC6861 in the Telescopium galaxy group (AS0851) to probe the interaction
history between these galaxies. Mean surface brightness profiles for NGC6868
and NGC6861 are each well described by double beta-models, suggesting that they
are each the dominant galaxy in a galaxy subgroup about to merge. Surface
brightness and temperature maps of the brightest group galaxy NGC6868 show a
cold front edge ~23 kpc to the north, and a cool 0.62 keV spiral-shaped tail to
the south. Analysis of the temperature and density across the cold front
constrains the relative motion between NGC6868 and the ambient group gas to be
at most transonic; while the spiral morphology of the tail strongly suggests
that the cold front edge and tail are the result of gas sloshing due to the
subgroup merger. The cooler central region of NGC6861 is surrounded by a sheath
of hot gas to the east and hot, bifurcated tails of X-ray emission to the west
and northwest. We discuss supersonic infall of the NGC6861 subroup, sloshing
from the NGC6868 and NGC6861 subgroup merger, and AGN heating as possible
explanations for these features, and discuss possible scenarios that may
contribute to the order of magnitude discrepancy between the Margorrian and
black hole mass - sigma predictions for its central black hole.
