Ionized Gas in the Galactic Center: New Observations and Interpretation

TL;DR

This study provides new high-resolution observations of ionized gas in the Galactic Center, revealing a spiral pattern and suggesting a one-armed spiral density wave as the underlying physical mechanism.

Contribution

It introduces improved observational data and interprets the gas dynamics as a spiral density wave, contrasting with previous models of linear feature motion.

Findings

Gas orbits are nearly circular with a small inward velocity.

The spatial distribution fits a spiral pattern.

A one-armed spiral density wave explains the kinematics.

Abstract

We present new observations of the [Ne II] emission from the ionized gas in Sgr A West with improved resolution and sensitivity. About half of the emission comes from gas with kinematics indicating it is orbiting in a plane tipped about 25\degree\ from the Galactic plane. This plane is consistent with that derived previously for the circumnuclear molecular disk and the northern arm and western arc ionized features. However, unlike most previous studies, we conclude that the ionized gas is not moving along the ionized features, but on more nearly circular paths. The observed speeds are close to, but probably somewhat less than expected for orbital motions in the potential of the central black hole and stars and have a small inward component. The spatial distribution of the emission is well fitted by a spiral pattern. We discuss possible physical explanations for the spatial distribution and kinematics of the ionized gas, and conclude that both may be best explained by a one-armed spiral density wave, which also accounts for both the observed low velocities and the inward velocity component. We suggest that a density wave may result from the precession of elliptical orbits in the potential of the black hole and stellar mass distribution.