Massive Star Formation of the Sgr A East HII Regions Near the Galactic Center

TL;DR

This paper studies the massive star formation near the Galactic Center, focusing on ionized gas and the properties of a young O9-B0 star within the Sgr A East HII regions, revealing details about its ionization and kinematics.

Contribution

It provides detailed multi-wavelength observations and analysis of the ionized gas and the central massive star in the Sgr A East HII regions, highlighting the star's properties and the dynamics of the surrounding ionized material.

Findings

The central star is a young O9-B0 star with ~25 solar masses.

Ionized features D1 and D2 are likely ionized by UV radiation from the star.

The star's circumstellar disk photoevaporates in ~3x10^4 years, producing observed ionized gas.

Abstract

A group of four compact HII regions associated with the well-known 50 km/s molecular cloud is the closest site of on-going star formation to the dynamical center of the Galaxy, at a projected distance of ~6 pc. We present a study of ionized gas based on the [NeII] (12.8 micron) line, as well as multi-frequency radio continuum, HST Pa alpha and Spitzer IRAC observations of the most compact member of the HII group, Sgr A East HII D. The radio continuum image at 6cm shows that this source breaks up into two equally bright ionized features, D1 and D2. The SED of the D source is consistent with it being due to a 25\pm3 solar mass, star with a luminosity of 8\pm3x10^4 solar luminosity. The inferred mass, effective temperature of the UV source and the ionization rate are compatible with a young O9-B0 star. The ionized features D1 and D2 are considered to be ionized by UV radiation collimated by an accretion disk. We consider that the central massive star photoevaporates its circumstellar disk on a timescale of 3x10^4 years giving a mass flux ~3x10^{-5} solar mass per yr and producing the ionized material in D1 and D2 expanding in an inhomogeneous medium. The ionized gas kinematics, as traced by the [Ne II] emission, is difficult to interpret, but it could be explained by the interaction of a bipolar jet with surrounding gas along with what appears to to be a conical wall of lower velocity gas. The other HII regions, Sgr A East A-C, have morphologies and kinematics that more closely resemble cometary flows seen in other compact HII regions, where gas moves along a paraboloidal surface formed by the interaction of a stellar wind with a molecular cloud.