Computer Science
Scientific paper
Dec 1987
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1987phdt........37d&link_type=abstract
Thesis (PH.D.)--THE UNIVERSITY OF WISCONSIN - MADISON, 1987.Source: Dissertation Abstracts International, Volume: 49-01, Sectio
Computer Science
8
Interstellar
Scientific paper
Interstellar line data along lines of sight that extend beyond the galactic disk have been examined in order to investigate the nature of Milky Way halo gas. The primary objective of this research is to employ the additional kinematic information contained in the velocity profiles of high resolution ultraviolet absorption and 21-cm emission data toward a large sample of objects that lie in or beyond the halo of our galaxy. The first chapter contains a detailed study of the kinematics of halo gas at high lattitudes which includes the study of absorption toward objects with |b| > 40^circ where the effects of galactic rotation are minimized and the vertical motions peculiar the plane are emphasized. The second chapter presents the study of gas toward a larger sample of stars at a range of galactic latitudes that includes the data from the surveys of Savage and Massa (1987) and Pettini and West (1982). The final chapter presents a comparison between the results from the first two chapters and results from the study of absorption in the spectra of QSOs. At high latitudes, the data show large systematic velocities and a pronounced asymmetry between halo gas toward the NGP and SGP. In the north, substantial amounts of material of both low and high ionization states are seen to be falling in toward the disk, at velocities up to ~120 km/s in the most extreme case. Toward the south, low ionization state material shows no extreme or systematic motions but the data suggest that the highly ionized material may be, on the whole, flowing away from the disk. Much of the high velocity absorption toward the NGP can be explained by a large intermediate velocity HI feature that may be associated with a large high velocity cloud complex, but some cannot. Limits on the distance to several high velocity clouds (HVCs) are determined. Large scale convection of galactic disk gas, such as a galactic fountain model, is the favored interpretation. However, extragalactic infall cannot be ruled out. On the basis of the kinematics and ionization structure in the gas at large distances from the plane, it is concluded that Milky Way halo gas absorption does not resemble the narrow absorption seen toward the majority of QSOs.
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