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Neutral gas and the magnetic field in the Galactic Center

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Title: Neutral gas and the magnetic field in the Galactic Center
Author(s): Plante, Raymond Louis
Doctoral Committee Chair(s): Lo, K. Y.
Department / Program: Astronomy
Discipline: Astronomy
Degree Granting Institution: University of Illinois at Urbana-Champaign
Degree: Ph.D.
Genre: Dissertation
Subject(s): Physics, Astronomy and Astrophysics
Abstract: There is substantial evidence that the Galactic Center harbors some of the strongest observable magnetic fields in the Galaxy, which are expected to have a major role in the astrophysical processes there. In this thesis, I present results from an experiment to measure the line-of-sight component of the magnetic field, $B\sb\Vert$, via Zeeman splitting of the 21-cm line of neutral hydrogen. In addition, I report a 3$\sigma$ upper limit of 2 mG for $B\sb\Vert$ in the neutral hydrogen within the circumnuclear disk of M82.Milligauss fields were detected with the highest confidence from three regions within the northern portion of the circumnuclear gas approximately 2 pc from the Galactic Center. The measurement of $B\sb\Vert$ with the highest signal-to-noise ratio (S/N) was $-3.0\pm0.6$ mG which comes from the highest velocity component within the region. Marginal detections were made elsewhere in the circumnuclear gas; 3$\sigma$ upper-limits call for $\vert B\sb\Vert\vert\ <$ 2.5 mG for the circumnuclear gas and $\vert B\sb\Vert\vert\ <$ 0.9 mG for the giant molecular clouds associated with the Sgr A East shell.The distribution and kinematics of the H I gas were also studied. The signature of a rotating gas ring can be seen in the H I approximately 1 pc south of the inner edge of the molecular ring; considered in conjunction with results from dense gas observations, the ring implies an increasing rotation velocity for the disk for R = 2-3 pc. No clear indication of disk rotation can be seen in the H I gas north of the Sgr A*. Some of the gas displays streamer-like structures in position-velocity space. This may be indicative of tidal stretching of clouds in the differentially rotating disk or, alternatively, of gas infall along a highly eccentric orbit similar to the orbit inferred previously for the ionized gas streamer known as the northern arm. A model is suggested in which the H I gas north of Sgr A* is part of a massive infalling cloud, and evidence which supports this picture is discussed. Such a model implies that the infall would have as large an effect on the structural evolution of the large-scale poloidal magnetic field as the rotating circumnuclear disk.The observations confirm the presence of gas associated with M-0.02-0.07 in front of the Sgr A East shell: the previously observed blue shifted gas and both components of the red shifted gas are seen. The H I gas is found to be quite clumpy and demonstrates small-scale variations in bulk velocity over large scale gradients. In general, the H I distribution is consistent with the picture suggested by Serabyn et al. (1992, Astrophys. J., 395, 166) based on observations of the dense gas in which Sgr A East shell is expanding into the neighboring molecular cloud.
Issue Date: 1995
Type: Text
Language: English
URI: http://hdl.handle.net/2142/19063
Rights Information: Copyright 1995 Plante, Raymond Louis
Date Available in IDEALS: 2011-05-07
Identifier in Online Catalog: AAI9522160
OCLC Identifier: (UMI)AAI9522160
 

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