Fast and Furious: Shock Heated Gas as the Origin of Spatially Resolved
  Hard X-ray Emission in the Central 5 kpc of the Galaxy Merger NGC 6240
  We have obtained a deep, sub-arcsecond resolution X-ray image of the nuclear
region of the luminous galaxy merger NGC 6240 with Chandra, which resolves the
X-ray emission from the pair of active nuclei and the diffuse hot gas in great
detail. We detect extended hard X-ray emission from kT~6 keV (~70 million K)
hot gas over a spatial scale of 5 kpc, indicating the presence of fast shocks
with velocity of ~2200 km/s. For the first time we obtain the spatial
distribution of this highly ionized gas emitting FeXXV, which shows a
remarkable correspondence to the large scale morphology of H_2(1-0) S(1) line
emission and H\alpha filaments. Propagation of fast shocks originated in the
starburst driven wind into the ambient dense gas can account for this
morphological correspondence. With an observed L(0.5-8 keV)=5.3E+41 erg/s, the
diffuse hard X-ray emission is 100 times more luminous than that observed in
the classic starburst galaxy M82. Assuming a filling factor of 1% for the 70 MK
temperature gas, we estimate its total mass (M_{hot}=1.8E+8 Msun) and thermal
energy (E_{th}=6.5E+57 ergs). The total iron mass in the highly ionized plasma
is M_{Fe}=4.6E+5 Msun. Both the energetics and the iron mass in the hot gas are
consistent with the expected injection from the supernovae explosion during the
starburst that is commensurate with its high star formation rate. No evidence
for fluorescent Fe I emission is found in the CO filament connecting the two
nuclei.
