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      https://www.ias.ac.in/article/fulltext/joaa/025/03-04/0129-0141

    • Keywords

       

      Galaxy: nucleus; radio lines: ISM

    • 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.

    • Author Affiliations

       

      K. S. Dwarakanath1 W. M. Goss2 J. H. Zhao3 C. C. Lang4

      1. Raman Research Institute, Sadashivanagar, Bangalore - 560 080, India
      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
    • Dates

       
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