The Galactic Center 50-km s-1 Molecular Cloud with An Expanding Shell

Masato Tsuboi, Atsushi Miyazaki, Sachiko K. Okumura

(1) Institute of Space and Astronautical Science, Sagamihara, Kanagawa 229-8510
(2) Department of Astronomy, the University of Tokyo, Bunkyo, Tokyo 113-0033
(3) Mizusawa VERA Observatory, National Astronomical Observatory, Mizusawa, Oshu, Iwate 023-0861
(4) National Astronomical Observatory, Mitaka, Tokyo, 181-8588

Paper: PASJ Feb 2009, in press


We performed high-resolution observation of the Galactic Center 50-km s -1 molecular cloud in the CS J = 1-0 line using the Nobeyama Millimeter Array (NMA). The molecular cloud mainly has three different spatial components with large velocity widths up to 60 km s -1. The northwest component is located at an apparent contact point to the Sgr A east shell and elongated along the boundary of the shell. The large velocity width of the component is responsible for the interaction with the Sgr A east shell. The molecular gas distribution in CS line emission is dissimilar to that observed previously in NH3 line emissions. The appearances shows presumably the area of CS line emission enhanced by shock. The central and southwest components are located just out of the Sgr A east shell and far from it, respectively. However, these components have large velocity widths. We found a well-shaped circular molecular shell with expanding motion in the 50-km s-1 molecular cloud. This is responsible for the large velocity width. The continuum source in the expanding molecular shell has a steep spectrum in the mm-wave although this is not identified in the previous 5-GHz map. This source may be an SNR with an ionized sheath. From the aspect ratio of the expanding molecular shell of 1.1, the magnetic field in/around the shell is estimated to be smaller than 100 mu Gauss. The weak magnetic field is consistent with on-going active star formation in the 50-km s -1 molecular cloud. The comparison among CS line emission, low frequency continuum, and millimeter continuum toward the 50-km s -1 molecular cloud suggests a face-on view of the Sgr A region. The molecular cloud is located in the Sgr A halo region.

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