2012ApJ...755...25B

Chandra x-ray observations of NGC 4342, 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 D₂₅ ellipse is L_0.5-2 keV_= 2.7x10³⁹ 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 NGC 4342 moves through external gas. From the thermal pressure ratios inside and outside the cold front, we estimate the velocity of NGC 4342 and find that it moves supersonically (M ∼ 2.6) toward the northeast. Outside the optical extent of the galaxy, we detect ∼17 bright (L_0.5 - 8keV ≳ 3 x 10³⁷ erg/s) excess x-ray point sources. The excess sources are presumably LMXBs located in metal-poor globular clusters (GCs) in the extended dark matter halo of NGC 4342. Based on the number of excess sources and the average frequency of bright LMXBs in GCs, we estimate that NGC 4342 may host roughly 850-1700 GCs. In good agreement with this, optical observations hint that NGC 4342 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.