EDP Sciences
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Volume 408, Number 3, September IV 2003
Page(s) 1009 - 1014
Section Formation, structure and evolution of stars
DOI http://dx.doi.org/10.1051/0004-6361:20031033

A&A 408, 1009-1014 (2003)
DOI: 10.1051/0004-6361:20031033

The velocity field of ionized gas near Sgr A $^{\ast}$

H. S. Liszt

National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903-2475, USA
(Received 28 February 2003 / Accepted 2 July 2003 )

Several distinct kinematic patterns are superposed in the ionized gas seen nearest Sgr A $^{\ast}$, the compact radio source at the center of the Milky Way. This has led to confusion over the morphology and motions of the gas; the recent dispersion-ring model of Sanders (1998) inadvertantly elides parts of two separate features and reproduces a description of the gas flow which does not actually occur. We demonstrate the gas kinematics via an analysis of the high-resolution H92 $\alpha$ radio recombination line data of Roberts & Goss (1993) and Roberts et al. (1996). The characteristic kinematic pattern of the "Bar" is reproduced by rotation in near-polar orbits seen edge-on at distances of 0.3-0.8 pc from Sgr A $^{\ast}$, with larger radii seen to the east. The mass of ionized material in the Bar is ~ $27~{ M}_{\odot}$. The Bar and Eastern Arm together probably represent a single stream of gas falling on to the galactic center, crossing from east to west.

Key words: Galaxy: center -- radio lines: ISM

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