Neutral gas and the magnetic field in the Galactic Center
Plante, Raymond Louis
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https://hdl.handle.net/2142/19063
Description
Title
Neutral gas and the magnetic field in the Galactic Center
Author(s)
Plante, Raymond Louis
Issue Date
1995
Doctoral Committee Chair(s)
Lo, K.Y.
Department of Study
Astronomy
Discipline
Astronomy
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Physics, Astronomy and Astrophysics
Language
eng
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.
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