HighâResolution Imaging of Warm and Dense Molecular Gas in the Nuclear Region of the Luminous Infrared Galaxy NGC 6240
Journal Articles
Overview
Research
Identity
Additional Document Info
View All
Overview
abstract
We present ~2'' resolution CO(3-2), HCO+(4-3) and 880micron continuum images
of the luminous infrared galaxy NGC6240 obtained at the Submillimeter Array. We
find that the spatially resolved CO(3-2), HCO+(4-3) and the 880micron emission
peaks between the two nuclear components that are both known to harbor AGNs.
Our Large Velocity Gradient (LVG) analysis performed on each velocity channel
suggests that the peak of the molecular gas emission traced in our observations
is warm (T = 20 - 100K), dense (nH2 = 10^(5.0 - 5.4) cm^-3) and moderately
optically thin (tau = 0.2 - 2) in the central 1 kpc. We also find large column
densities of ~10^(23) cm^(-2). Such extreme conditions are observed over ~300
km s^(-1) centered around the CO derived systemic velocity. The derived
molecular gas mass from the CO(3-2) emission and a CO-to-H2 conversion factor
commonly used for ULIRGs is (6.9 +/- 1.7) x 10^9 Msun, and this is consistent
with the mass derived from previous CO(2-1) observations. The gas is highly
turbulent in the central kpc (Delta v_(FWZI) ~ 1175 km s^(-1)). Furthermore,
possible inflow or outflow activity is suggested from the CO(3-2) velocity
distribution. We tentatively state that 3.5 x 10^8 Msun of isolated CO(3-2)
emission seen west of the northern disk may be associated with outflows from
starburst superwinds, but the gas outflow scenario from one of the central AGN
is not completely ruled out. Piecing all of the information together, the
central region of NGC 6240 harbors 2 AGNs, ~10^(10) Msun of molecular gas mass,
5 x 10^7 Msun of dust mass, and has possible evidence of inflow and outflow
activity.
