Gas Dynamics in the Non-barred Seyfert Galaxy NGC 4501

Abstract

We report high resolution interferometer observations of the central 5 kpc region of NGC 4501. The observations were carried out in CO line using the Nobeyama Millimeter Array (NMA). The CO major features are (1) a nuclear concentration which consists of double peaks, (2) spiral arms. The feature (1) has a low star-forming efficiency, which might be due to low gas- to-dynamical mass ratio. The central double peaks are located on the root of optical spiral arms in a HST image. The spiral arms are extending out from the nuclear region, and they show systematic non-circular motions. They seem to be associated with the HST spiral dust lanes and may be linked to the central double peaks. We calculated gas cloud orbits in a stellar spiral potential, and could explain the observed CO spiral arms and non-circular motion in the arms. In a stellar spiral potential, two mechanisms of angular momentum transfer are possible — galactic spiral shocks in orbit-crowding regions, and gravitational torques exerted by the stellar spirals. We found that the galactic shock is dominant. These mechanisms lead to gas inflow which possibly explains the central-condensed double peaks in NGC 4501.