NMA CO (J=1-0) Observations of the Halpha/Radio Lobe Galaxy NGC 3079: Gas Dynamics in a Weak Bar Potential and Central Massive Core

Abstract

within 24 lines with 80 characters) We present ^12CO (1-0) observations in the central 4.5 kpc (1 arcmin) of the Halpha/Radio lobe galaxy NGC 3079 with the Nobeyama Millimeter Array. The molecular gas shows four components: a main disk, spiral arms, a nuclear disk, and a nuclear core. The main disk extends beyond our spatial coverage. The spiral arms are superimposed on the main disk. The nuclear disk with about 600 pc radius has an intense concentration of molecular gas. Its appearance on PV diagrams is indicative of oval motions of the gas, rather than circular. The nuclear core is more compact than our resolution. Though it is unresolved, the nuclear core shows a very high velocity about 200 km/s even at the radius of about 100 pc on the PV diagram. We propose a model that NGC 3079 contains a weak bar. This model explains the observed features: the main disk and spiral arms result from gaseous x1-orbits and associated crowding respectively. The nuclear disk arises from gaseous x2-orbits. From the appearance of the spiral arms on the PV diagram, the pattern speed of the bar is estimated to be 55+-10 km/s/kpc. The high velocity of the nuclear core cannot be explained by our model for a bar. Thus we attribute it to a central massive core with a dynamical mass of 10^9 Msun within the central 100 pc. This mass is three orders of magnitude more massive than that of a central black hole in this galaxy.