Abstract
We have observed the infrared-luminous galaxy NGC 6240 using a long- slit near-IR spectrometer. The very strong 1-0 5(1) line of molecular hydrogen (H_2_) is extended over about 9" and shows a distinct component of emission extending to the south-east of the nucleus, with a velocity of about 300 km s^-1^ lower than the diffuse nuclear emission. We find only very weak emission in the 5-3 O(3) and 6-4 Q(1) lines of H_2_(1.61 micron), suggesting little contribution from fluorescently excited H_2_. Fe II (1.644 micron) emission, which requires stronger shocks to excite than the 1-0 S(1) line, is slightly more concentrated and displaced to the north of the nucleus and shows a different velocity structure than the S(1) line. We find no strong Brγ emission from the nucleus but some weak patches of extranuclear emission are probably detected. We suggest that the strong H_2_ emission is due to slow shocks being driven into molecular clouds by the collision of the clouds with the diffuse interstellar medium (ISM) of the other galaxy in this merging system.
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