Gasdynamics in the LINER galaxy NGC 5005: episodic fueling of a nuclear disk.
SAKAMOTO K., BAKER A.J. and SCOVILLE N.Z.
Abstract (from CDS):
We report high-resolution CO(1-0) observations in the central 6 kpc (1') of the LINER galaxy NGC 5005 with the Owens Valley Radio Observatory millimeter array. Molecular gas is distributed in three components–a ring at a radius of about 3 kpc, a strong central condensation, and a stream to the northwest of the nucleus but inside the 3 kpc ring. The ring shows systematic noncircular motions, with apparent inward velocities of ∼50 km.s–1 on the minor axis. The central condensation is a disk of ∼1 kpc radius with a central depression of ∼50 pc radius. This disk has a molecular gas mass of ∼2x109 M☉; it shows a steep velocity gradient and a velocity range (∼750 km.s–1) 30% larger than the velocity width of the rest of the galaxy. The stream between the 3 kpc ring and the nuclear disk lies on a straight dust lane seen in the optical. If this material moves in the plane of the galaxy, it lies at a radius of ∼1 kpc but has a velocity offset by up to ∼150 km.s–1 from galactic rotation. We suggest that an optically inconspicuous stellar bar lying within the 3 kpc ring can explain the observed gasdynamics. This bar is expected to connect the nuclear disk and the ring along the position angle of the northwest stream. A position-velocity cut in this direction reveals features that match the characteristic motions of gas in a barred potential. Our model indicates that gas in the northwest stream is on an x1 orbit at the bar's leading edge; it is falling into the nucleus with a large noncircular velocity and will eventually contribute ∼2x108 M☉ to the nuclear disk. If most of this material merges with the disk on its first passage of pericenter, the gas accretion rate during the collision will be ∼50 M☉.yr–1. We associate the disk with an inner 2:1 Lindblad resonance and attribute its large line width to favorably oriented elliptical orbits rather than (necessarily) to a large central mass. The 3 kpc ring is likely an inner 4:1 Lindblad resonance ring–or a pair of tightly wound spiral arms–arising at the bar ends. Both scenarios can explain the apparent noncircular motions in the ring. The high rate of bar-driven inflow and the irregular appearance of the northwest stream suggest that a major fueling event is in progress in NGC 5005. Such episodic (rather than continuous) gas supply can regulate the triggering of starburst and accretion activity in galactic nuclei.
Galaxies: Active - Galaxies: ISM - Galaxies: Kinematics and Dynamics - Galaxies: Spiral - Galaxies: Starburst