Chandra observations of NGC4342, an optically faint, X-ray gas-rich
  early-type galaxy
  Chandra X-ray observations of NGC4342, a low stellar mass (M_K=-22.79 mag)
early-type galaxy, show luminous, diffuse X-ray emission originating from hot
gas with temperature of kT~0.6 keV. The observed 0.5-2 keV band luminosity of
the diffuse X-ray emission within the D_25 ellipse is L_0.5-2keV = 2.7 x 10^39
erg/s. The hot gas has a significantly broader distribution than the stellar
light, and shows strong hydrodynamic disturbances with a sharp surface
brightness edge to the northeast and a trailing tail. We identify the edge as a
cold front and conclude that the distorted morphology of the hot gas is
produced by ram pressure as NGC4342 moves through external gas. From the
thermal pressure ratios inside and outside the cold front, we estimate the
velocity of NGC4342 and find that it moves supersonically (M~2.6) towards the
northeast. Outside the optical extent of the galaxy we detect ~17 bright
(L_0.5-8keV > 3 x 10^37 erg/s) excess X-ray point sources. The excess sources
are presumably low-mass X-ray binaries (LMXBs) located in metal-poor globular
clusters (GCs) in the extended dark matter halo of NGC4342. Based on the number
of excess sources and the average frequency of bright LMXBs in GCs, we estimate
that NGC4342 may host roughly 850-1700 GCs. In good agreement with this,
optical observations hint that NGC4342 may harbor 1200 +/- 500 GCs. This number
corresponds to a GC specific frequency of S_N = 19.9 +/- 8.3, which is among
the largest values observed in full-size galaxies.
