Observations of the Hα/radio Lobe Galaxy Ngc 3079: Gas Dynamics in a Weak Bar Potential and Central Massive Core

We present CO (1-0) observations in the central 4.5 kpc (1) of the Hα/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 along the galaxy major axis. We detected its central 2 kpc radius, while its full extent is beyond our spatial coverage. Molecular gas is smoothly distributed in the main disk, having a gas mass of 5× 10M⊙ within the central ∼ 2 kpc radius. The spiral arms are superimposed on the main disk. Abrupt velocity changes of up to ∼ 200 km s are observed along the spiral arms in S-shaped twists of isovelocity contours and double velocity-peaked features on the spectra. The nuclear disk with ∼ 600 pc radius appears in position-velocity (PV) diagrams, having an intense concentration of molecular gas. Its appearance on PV diagrams is indicative of oval motions of the gas, rather than circular. The nuclear disk and spiral arms form the so-called “figure-of-eight” pattern on a PV diagram. The nuclear core is more compact than our current resolution (2 = 150 pc), and has a gas mass of 3×10M⊙ within the central 150 pc. Though it is unresolved, the nuclear core shows a very high velocity ∼ 200 km s even at the radius of ∼ 100 pc on the PV diagram. We propose a model that NGC 3079 contains a weak bar. The weak bar model explains the observed features of the main disk, spiral arms, and nuclear JSPS Research Fellow; E-mail: [email protected] Institute of Astronomy, University of Tokyo, Mitaka, Tokyo 181-0015, Japan Nobeyama Radio Observatory, Minamisaku, Nagano, 384-1305, Japan Department of Physics, Queen’s University, Kingston, Ontario, K7L3N6, Canada