Superwind-driven Intense H2Emission in NGC 6240. II. Detailed Comparison of Kinematic and Morphological Structures of the Warm and Cold Molecular Gas

We report on our new analysis of the spatial and kinematical distribution ofwarm and cold molecular gas in NGC 6240, which was undertaken to explore theorigin of its unusually luminous H$_2$ emission. By comparing three-dimensionalemission-line data (in space and velocity) of CO (J=2-1) in the radio and H$_2$in the near infrared, we are able to study the H$_2$ emitting efficiency,defined in terms of the intensity ratio of H$_2$ to CO [$I$(H$_2$)/$I$(CO)], asa function of velocity. The integrated H$_2$ emitting efficiency is calculatedby integrating the velocity profile of H$_2$ emitting efficiency in blue, red,and total (blue + red) velocity regions of the profile. We find that (1) boththe total H$_2$ emitting efficiency and the blue-to-red ratio of the efficiencyare larger in regions surrounding the CO and H$_2$ intensity peaks, and (2) theH$_2$ emitting efficiency and the kinematical conditions in the warm moleculargas are closely related to each other. A collision between the molecular gasconcentration and the external superwind outflow from the southern nucleusseems plausible to explain these characteristics, since it can reproduce theenhanced emitting efficiency of blueshifted H$_2$ around the molecular gasconcentration, if we assume that the superwind blows from the southern nucleustoward us, hitting the entire gas concentration from behind. In this model,internal cloud-cloud collisions within the molecular gas concentration areenhanced by the interaction with the superwind outflow, and efficient andintense shock-excited H$_2$ emission is expected as a result of thecloud-crushing mechanism.Comment: 12 pages, 6 figures, accepted for publication in A