The velocity field of ionized gas near Sgr A

National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903-2475, USA

Corresponding author: hliszt@nrao.edu

Received: 28 February 2003
Accepted: 2 July 2003

Abstract

Several distinct kinematic patterns are superposed in the ionized gas seen nearest Sgr A, 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 H92α 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, with larger radii seen to the east. The mass of ionized material in the Bar is ~. The Bar and Eastern Arm together probably represent a single stream of gas falling on to the galactic center, crossing from east to west.