This thesis presents a kinematical study of the molecular gas and dust in thenearby radio galaxy Centaurus A (NGC 5128) and the nearby starburst M82.
The CO (2-1) emission along the inner dust lane of Centaurus A, observedwith the Caltech Submillimeter Observatory on Mauna Kea, shows the moleculargas to be in a thin disk, with a velocity dispersion of only about 10 km s^(-1) . Theobserved line profiles are broadened considerably due to beam smearing of thegas velocity field. The profile shapes are inconsistent with planar circular andnoncircular motion. However, a warped disk in a prolate potential provides agood fit to the profile shapes. The morphology and kinematics of the moleculargas is similar to that of the ionized material, seen in Ha. The best fitting warpeddisk model not only matches the optical appearance of the dustlane, but alsoagrees with the large scale map of the CO emission, and is consistent with HImeasurements at larger radii.
We present infrared images of Cen A (NGC5128) in the J,H, and K bandsobserved with the 1.5 m telescope at CTIO. The infrared morphology is primarilydetermined by the presence of a thin absorptive warped disk. By integrating thelight of the underlying prolate galaxy through such a disk, we construct modelswhich we compare with infrared and X-ray data. The geometry of the warped diskneeded to fit the IR data is consistent with a warped disk which has evolved as aresult of differential precession in a prolate potential. The disk has an inclination,with respect to the principal axis of the underlying elliptical galaxy, that is higherat large radii than in the inner region.
A scenario is proposed where a small gas rich galaxy infalling under the forceof dynamical friction is tidally stripped. Stripping occurs at different times duringits infall. The orientation of the resulting gas disk depends upon the angularmomentum of the infalling galaxy. We find that the resulting precession angle ofthe disk is well described by the precession model, but that the inclination anglemay vary as a function of radius. We propose an orbit for the infalling galaxythat is consistent with the geometry of the warped disk needed to fit our infrareddata, rotation observed in the outer part of the galaxy and the location of thestellar shells in the same region.
We model the kinematics of the molecular gas in the nearly edge-on diskm M82, by considering velocity and surface density perturbations caused by apossible rotating kpc long bar. A model with a bar that has an Inner LinbladResonance at r ~ 10" ~ 150 pc fits the molecular observations of the inner torus.This model is consistent with the angle of the bar inferred from the K (2.2µm)isophotes. The clouds have a cloud-cloud velocity dispersion of ~ 30 km s^(-1) implyingthat the disk is unstable to short timescale axisymmetric perturbations.This is consistent with the hypothesis that the high star formation efficiencies instarbursts are due to the the short timescales of gravitational instability. It islikely that the bar has mediated the starburst.
There are serious deviations from our model at large radii. It is likely thatthere are two components of molecular material which were not considered by ourmodel: (i) a component at large radii that is in the galactic plane and has lowline-of-sight velocities due to a larger scale bar or due to the fact that there isa lack of molecular gas over a large range of radius (perhaps due to a previousinteraction which caused a large fraction of the gas to sink into the nucleus),and (ii) a molecular wind with velocities of the order of the observed line widths(80 - 120 km s^(-1)). While dense gas can be accelerated in a galactic superwind tovelocities of this order of magnitude, it is unclear how this gas interacts with thesuperwind.
