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

Journal of astrophysics and astronomy

C. C. Lang4¹  J. H. Zhao3²  K. S. Dwarakanath1³  W. M. Goss2⁴ 

[1] Department of Physics and Astronomy, University of Iowa, Iowa City, IA 52242.$$;Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138.$$;Raman Research Institute, Sadashivanagar, Bangalore 560 080, India.$$;National Radio Astronomy Observatory, PO BOX O, Socorro, NM 87801.$$

关键词: Galaxy: nucleus;    radio lines: ISM.;   

DOI  :  

学科分类：天文学(综合)

来源: Indian Academy of Sciences

【 摘 要 】

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 𝑉lsr = -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.

【 授权许可】

Unknown