On the Origin of the Wide HI Absorption Line Toward Sgr

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 of ∼ 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 Vlsr = –4 ± 15 km s . The mean full width at half maximum is 119 ± 42 km s. Such a wide line is absent in e-mail:[email protected] e-mail:[email protected] email:[email protected] email:[email protected] 1 2 Dwarakanath, Goss, Zhao & Lang the spectra at positions beyond ∼ 2 from Sgr A*. The positionvelocity 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.