The High-Density Ionized Gas in the Central Parsec of the Galaxy

We report a study of the H30$alpha$ line emission at 1.3 mm from the region around Sgr A* made with the Submillimeter Array at a resolution of 2arcsec over a field of 60arcsec (2 parsec) and a velocity range of -360 to +345 kms. This field encompasses most of the Galactic centers minispiral. With an isothermal homogeneous HII model, we determined the physical conditions of the ionized gas at specific locations in the Northern and Eastern Arms from the H30$alpha$ line data along with Very Large Array data from the H92$alpha$ line at 3.6 cm and from the radio continuum emission at 1.3 cm. The typical electron density and kinetic temperature in the minispiral arms are 3-21$times10^4$ cm$^{-3}$ and 5,000-13,000 K, respectively. The H30$alpha$ and H92$alpha$ line profiles are broadened due to the large velocity shear within and along the beam produced by dynamical motions in the strong gravitational field near Sgr A*. We constructed a 3D model of the minispiral using the orbital parameters derived under the assumptions that the gas flows are in Keplerian motion. The gas in the Eastern Arm appears to collide with the Northern Arm flow in the Bar region, which is located 0.1-0.2 parsec south of and behind Sgr A*. Finally, a total Lyman continuum flux of $3times10^{50}$ photons s$^{-1}$ is inferred from the assumption that the gas is photoionized and the ionizing photons for the high-density gas in the minispiral arms are from external sources, which is equivalent to $sim250$ O9-type zero-age-main-sequence stars.

The High-Density Ionized Gas in the Central Parsecs of the Galaxy

We report the results from observations of H30$alpha$ line emission in Sgr A West with the Submillimeter Array at a resolution of 2arcsec and a field of view of about 40arcsec. The H30$alpha$ line is sensitive to the high-density ionized gas in the minispiral structure. We compare the velocity field obtained from H30$alpha$ line emission to a Keplerian model, and our results suggest that the supermassive black hole at Sgr A* dominates the dynamics of the ionized gas. However, we also detect significant deviations from the Keplerian motion, which show that the impact of strong stellar winds from the massive stars along the ionized flows and the interaction between Northern and Eastern arms play significant roles in the local gas dynamics.