Investigations of Extragalactic Hydroxyl.
Abstract
Observations of extragalactic hydroxyl (OH) probe the physical conditions of galactic nuclear regions. The four 18 cm spectral lines of OH are known to respond differently to various conditions, possibly making hydroxyl a better probe then CO and HI in certain galaxies. First, OH must be detected; this thesis presents the results of an extensive survey for extragalactic hydroxyl using the Arecibo telescope. The OH is observed in absorption and in Megamaser emission but not in thermal emission despite low noise values. This survey was used as the basis for a statistical study between OH content and other parameters of the parent galaxy. Statistical methods for samples with upper limits were used to find correlations between (tau)(,OH) and the Hubble Type, IRAS colors, infrared luminosity, and IR-to -blue luminosity ratio of the galaxy. Two galaxies were then studied in detail using the Very Large Array (VLA) interferometer. The first was NGC 3628, an edge-on spiral galaxy in the Leo Triplet. The OH and HI absorption maps reveal a rotating disk which may follow the inner portion of the galaxy's rotation curve. A second structure which is expanding with respect to the disk is also revealed and may be similar to the three kpc arm in our own Galaxy. The second galaxy studied with the VLA was Mrk 273, a Seyfert with HI absorption and OH Megamaser emission. Although the continuum is resolved at 18 cm (and is a double at six cm), the absorption and emission are associated only with one component and, therefore, not resolved. So, unfortunately, no information on the disk rotation properties of this galaxy could be determined. This is very different from the VLA results for the prototype Megamaser in IC 4553 where the OH emission actually mimics the resolved continuum structure. Therefore, these observations could not be used to support the present Megamaser model.
- Publication:
-
Ph.D. Thesis
- Pub Date:
- 1987
- Bibcode:
- 1987PhDT.........2S
- Keywords:
-
- Physics: Astronomy and Astrophysics;
- Absorption Spectra;
- Emission Spectra;
- Galactic Nuclei;
- Galactic Radiation;
- Hydroxyl Radicals;
- Line Spectra;
- Galactic Rotation;
- Hubble Diagram;
- Infrared Radiation;
- Luminosity;
- Astrophysics