The First Measurement of Radial Acceleration of Ionized Gas Near Sagittarius A*

Motivated by the presence of a massive black hole coincident with Sgr A* at the center of our Galaxy, a number of observers have successfully detected proper motion of ionized gas and stars at the Galactic center. Here we compare the radial velocities of ionized gas in the inner parsec of the Galaxy in three epochs (1993, 1999 & 2002). VLA observations were carried out in the H92α radio recombination line from Sgr A West; each observation had identical velocity coverage as well as velocity and spatial resolutions. Accurate velocity fields were derived from Gaussian fitting the data from the three epochs; radial acceleration was determined by comparing the fitted velocity fields. In the Northern Arm of Sgr A West, we report the the detection of radial acceleration (+0.21 kms^-1 yr^-1) consistent with motion dominated by gravity. In the minicavity, the measured acceleration is too large to be the result of gravity alone and suggest that non-gravitational effects are significant. Additionally, we detect a single region that shows peculiar motion of +4.1 kms^-1 yr^-1 southeast of Sgr A*. The first evidence of the acceleration of ionized gas in the Galactic center is presented.