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Title:
VLA OH Observations of High Negative Velocity Gas toward Sagittarius A West: A High-Velocity Cloud Interacting with the Galactic Center
Authors:
Zhao, Jun-Hui; Goss, W. M.; Ho, Paul T. P.
Publication:
Astrophysical Journal v.450, p.122 (ApJ Homepage)
Publication Date:
09/1995
Origin:
APJ; KNUDSEN
Astronomy Keywords:
GALAXY: CENTER, ISM: CLOUDS, ISM: KINEMATICS AND DYNAMICS, RADIO LINES: ISM
DOI:
10.1086/176124
Bibliographic Code:
1995ApJ...450..122Z

Abstract

The high negative velocity cloud in the direction of Sgr A* at -180 km s-1 was discussed by Güsten & Downes (1981) more than a decade ago. Since then, numerous observations have been carried out to determine the properties of this component; however, the nature of this feature was uncertain due to the lack of high angular resolution observations. Recently, we have carried out VLA observations of this feature in the H I and OH lines at VLSR = -180 km s 1 with an angular resolution of several arcseconds. The OH 1667 MHz absorption is the best tracer of the gas in front of the continuum sources in the Galactic center. Both the structure and the kinematics have been determined, and we show that the high negative velocity absorbing gas is well mixed with the ionized gas in the center of the Galaxy. The mass of neutral gas seen in absorption at -180 km s-1 is about 5 × 103 Msun, only a small fraction of the entire cloud observed in CO emission. The observed kinematics are not consistent with ejection; outflow, or a possible association with the expanding molecular ring at V = -135 km s-1. The location and morphology suggest that this high-velocity cloud may be tidally disrupted. Based on a numerical model, we demonstrate that the disrupted high-velocity gas can flow toward the Galactic center and interact with the central gravitational potential, thereby distorting the kinematics of the high-velocity gas projected in front of Sgr A West. This model also suggests that the mini-cavity 3" southeast of Sgr A* could have resulted from the impact of a high negative velocity streamer. Both the morphology and the kinematics calculated in this model are consistent with the H92alpha observations of the central 10" of the Galaxy as published by Roberts, Yusef-Zadeh, & Goss (1995).

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