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

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.

29 pages, 9 figures, accepted by ApJ

References in corpus (6)

• Theory of Star Formation
• HST/NICMOS Paschen-alpha Survey of the Galactic Center: Overview
• Point Sources from a Spitzer IRAC Survey of the Galactic Center
• An equatorial wind from the massive young stellar object S140 IRS 1
• [Ne II] Observations of Gas Motions in Compact and Ultracompact H II Regions
• The Mid-Infrared Colors of the ISM and Extended Sources at the Galactic Center

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• Detection of Widespread Hot Ammonia in the Galactic Center
• Extraterrestrial Axion Search with the Breakthrough Listen Galactic Center Survey
• A Census of Early Phase High-Mass Star Formation in the Central Molecular Zone
• Cloud-cloud Collision in the Galactic Center 50 km s${}^{-1}$ Molecular Cloud
• Properties of the Compact HII Region Complex G-0.02-0.07
• Constraining the population of isolated massive stars within the Central Molecular Zone
• Statistical Properties of Molecular Clumps in the Galactic Center 50 km s${}^{-1}$ Molecular Cloud
• SOFIA/FORCAST Galactic Center Legacy Survey: Overview
• Signatures of Young Star Formation Activity Within Two Parsecs of Sgr A*
• The CARMA 3mm Survey of the Inner $0.7^{\circ }\times 0.4^{\circ }$ of the Central Molecular Zone
• Molecular Cloud Cores in the Galactic Center 50 $\mathrm{km}{\mathrm{s}}^{-1}$ Molecular Cloud
• Dusty Cradles in a Turbulent Nursery: The Sgr A East HII Region Complex at the Galactic Center
• G-0.02-0.07, the Compact HII Region Complex nearest to the Galactic Center with ALMA
• Hot Molecular Core Candidates in the Galactic Center 50 km/s Molecular Cloud
• The Galactic Center Black Hole Laboratory
• Hydroxyl, water, ammonia, carbon monoxide and neutral carbon towards the Sgr A complex