Superwind-driven Intense H2 Emission in NGC 6240 II: Detailed Comparison of Kinematical and Morphological Structures of the Warm and Cold Molecular Gas
Abstract
We report on our new analysis of the spatial and kinematical distribution of warm and cold molecular gas in NGC 6240, which was undertaken to explore the origin of its unusually luminous H2 emission. By comparing three-dimensional emission-line data (in space and velocity) of CO (J=2-1) in the radio and H2 in the near infrared, we are able to study the H2 emitting efficiency, defined in terms of the intensity ratio of H2 to CO [I(H2)/I(CO)], as a function of velocity. The integrated H2 emitting efficiency is calculated by integrating the velocity profile of H2 emitting efficiency in blue, red, and total (blue + red) velocity regions of the profile. We find that (1) both the total H2 emitting efficiency and the blue-to-red ratio of the efficiency are larger in regions surrounding the CO and H2 intensity peaks, and (2) the H2 emitting efficiency and the kinematical conditions in the warm molecular gas are closely related to each other. A collision between the molecular gas concentration and the external superwind outflow from the southern nucleus seems plausible to explain these characteristics, since it can reproduce the enhanced emitting efficiency of blueshifted H2 around the molecular gas concentration, if we assume that the superwind blows from the southern nucleus toward us, hitting the entire gas concentration from behind. In this model, internal cloud-cloud collisions within the molecular gas concentration are enhanced by the interaction with the superwind outflow, and efficient and intense shock-excited H2 emission is expected as a result of the cloud-crushing mechanism.
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