High Resolution CO(3-2) and HCO+(4-3) Imaging of the Luminous Infrared Galaxy NGC 6240

[[abstract]]We present interferometric CO(3-2), HCO+(4-3) and 870 micron continuum images of the luminous infrared galaxy NGC 6240 obtained at the Submillimeter Array (SMA). Our spatially resolved CO(3-2) and HCO+(4-3) emission peaks between the two nuclear components that are known to both harbour AGNs. We analyze the physical properties of the molecular gas in the nuclear starburst region using a Large Velocity Gradient (LVG) analysis. The LVG analysis performed on each 50 km/s channel using the CO(3-2), CO(1-0), HCO+(4-3), and HCO+(1-0) data cubes suggests that the peak of the molecular gas emission traced in our observations is warm (T = 20 - 200 K), dense (n[H2] = 10 4.5 - 5.3 cm-3 ) and optically thin (tau = 0.01 - 2) in the densest regions of the central 1 kpc. The average density in the central 2 kpc is n[H2] = 10 4.0 cm-3 , and the gas is highly turbulent there (Delta v[FWZI] ˜ 900 km/s). The derived molecular gas mass in the central 0.5 kpc (1.5 x 109 Msun) is consistent with the mass derived from previous CO(2-1) observations. We suggest that 4.0 x 108 Msun of isolated CO (3-2) emission seen west of the northern disk may be a direct consequence of gas outflow from the central AGN, which is a phenomenon seen in the latest numerical simulations that include black holes. Piecing the multi-wavelength information together, the central region of NGC 6240 harbours 2 AGNs, ˜109 Msun of molecular gas mass, and 5 x 107 Msun of dust mass, all contributing to the significant far infrared luminosity which is mostly due to starbursts induced by the merger[[fileno]]2010504020005[[department]]天文