Molecular Gas in Nearby Active Galactic Nuclei

Citation

Baker, Andrew Jordan (2000) Molecular Gas in Nearby Active Galactic Nuclei. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/c2qn-2b77. https://resolver.caltech.edu/CaltechETD:etd-09202008-104918

Abstract

This thesis describes the distributions, physical conditions, and kinematics of the molecular gas in eight nearby galaxies whose Seyfert and LINER nuclei display broad Hα emission. We have mapped these systems at a linear resolution of ~ 100 pc in the CO(2-1) rotational transition, as well as at lower resolution in the CO(1-0) line, using the Owens Valley Radio Observatory millimeter array. Subsequent kinematical modelling allows us to improve on this angular resolution by exploiting our high effective velocity resolution; we simultaneously determine the radial emissivity profile of each line and the velocity field which the gas traces. Analysis of the molecular emission from individual objects reveals (1) massive concentrations of molecular gas (~ 10⁹M☉) at small galactocentric radii (r ≤ 500 pc); (2) a pattern of high excitation at small radius, implied by variation in the ratio of CO (2-1) to CO(1-0) integrated intensities, which we attribute in part to the external heating of molecular clouds by energetic photons; (3) a high occurrence of nonaxisymmetric structures within 500 pc of the nucleus, including four gas bars; (4) evidence for episodic mass inflow along stellar bars outside 500 pc; and (5) apparent redirection of radio jets and ionizing photons from the nucleus by the molecular gas which they encounter. Our most striking discoveries are a dynamically decoupled secondary bar in the nucleus of NGC 7479, a mean integrated intensity ratio ≥ 1.85 in the nucleus of NGC 2681, and a warped molecular disk in the nucleus of NGC 1068.

Thesis Files