On the origin of the wide HI absorption line towards Sgr A* |
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| Authors: | K S Dwarakanath W M Goss J H Zhao C C Lang |
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| Institution: | (1) Raman Research Institute, Sadashivanagar, 560 080 Bangalore, India;(2) National Radio Astronomy Observatory, PO BOX O, 87801 Socorro, NM;(3) Harvard-Smithsonian Center for Astrophysics, 02138 Cambridge, MA;(4) Department of Physics and Astronomy, University of Iowa, 52242 Iowa City, IA |
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| Abstract: | We have imaged a region of ∼ 5′ extent surrounding Sgr A* in the HI 21 cm-line absorption using the Very Large Array. A Gaussian
decomposition of the optical depth spectra at positions within ∼ 2′ (∼ 5 pc at 8.5 kpc) of Sgr A* detects a wide line underlying
the many narrow absorption lines. The wide line has a mean peak optical depth of 0.32 ± 0.12 centered at a mean velocity of
V1sr = −4 ± 15 km s{−1}. The mean full width at half maximum is 119 ± 42 km s−1. Such a wide line is absent in the spectra at positions beyond ∼ 2′ from Sgr A*. The position-velocity diagrams in optical
depth reveal that the wide line originates in various components of the circumnuclear disk (radius ∼ 1.3′ ) surrounding Sgr
A*. These components contribute to the optical depth of the wide line in different velocity ranges. The position-velocity
diagrams do not reveal any diffuse feature which could be attributed to a large number of HI clouds along the line of sight
to Sgr A*. Consequently, the wide line has no implications either to a global population of shocked HI clouds in the Galaxy
or to the energetics of the interstellar medium as was earlier thought. |
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| Keywords: | Galaxy: nucleus radio lines: ISM |
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