2014ApJ...787...48X

We present Atacama Large Millimeter Array (ALMA) Cycle-0 observations of the CO (6-5) line emission (rest-frame frequency = 691.473 GHz) and of the 435 µm dust continuum emission in the nuclear region of NGC 34, a local luminous infrared galaxy at a distance of 84 Mpc (1'' = 407 pc) which contains a Seyfert 2 active galactic nucleus (AGN) and a nuclear starburst. The CO emission is well resolved by the ALMA beam (0.''26x0.''23), with an integrated flux of f_CO(6–5)= 1004 (± 151) Jy km/s. Both the morphology and kinematics of the CO (6-5) emission are rather regular, consistent with a compact rotating disk with a size of 200 pc. A significant emission feature is detected on the redshifted wing of the line profile at the frequency of the H¹³CN (8-7) line, with an integrated flux of 17.7±2.1(random)±2.7(systematic) Jy km/s. However, it cannot be ruled out that the feature is due to an outflow of warm dense gas with a mean velocity of 400 km/s. The continuum is resolved into an elongated configuration, and the observed flux corresponds to a dust mass of M_dust= 10^6.97±0.13 M_☉. An unresolved central core (radius ≃ 50 pc) contributes 28% of the continuum flux and 19% of the CO (6-5) flux, consistent with insignificant contributions of the AGN to both emissions. Both the CO (6-5) and continuum spatial distributions suggest a very high gas column density ( ≳ 10⁴ M_☉/pc2) in the nuclear region at radius ≲ 100 pc.