Astronomy and Astrophysics – Astrophysics
Scientific paper
Jan 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995phdt.........3p&link_type=abstract
Thesis (PH.D.)--UNIVERSITY OF ILLINOIS AT URBANA -CHAMPAIGN, 1995.Source: Dissertation Abstracts International, Volume: 56-03,
Astronomy and Astrophysics
Astrophysics
Scientific paper
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_ |, 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_ | 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_| with the highest signal-to-noise ratio (S/N) was -3.0+/-0.6 mG which comes from the highest velocity component within the region. Marginal detections were made elsewhere in the circumnuclear gas; 3sigma upper-limits call for | B_|| < 2.5 mG for the circumnuclear gas and | B_|| < 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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