On the Origin of the Wide HI Absorption Line Toward Sgr A*

K. S. Dwarakanath,1 W. M. Goss,2 J. H. Zhao3 & C. C. Lang4


(1) Raman Research Institute, Sadashivanagar, Bangalore 560 080,
(2) National Radio Astronomy Observatory, PO BOX O, Socorro, NM 87801,
(3) Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138,
(4) Department of Physics and Astronomy, University of Iowa, Iowa City, IA 52242

Paper: JAA (accepted)

EPrint Server: astro-ph/0408433


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 V_lsr = -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.


Preprints available from the authors at dwaraka@rri.res.in , or the raw TeX (no figures) if you click here.

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