G-0.02-0.07, the Compact HII Region Complex nearest to the Galactic Center with ALMA

Abstract

We have observed the compact HII region complex nearest to the dynamical center of the Galaxy, G-0.02-0.07, using ALMA in the H42a recombination line, CS J=2-1, H13CO+ J=1-0, and SiO v=0, J=2-1 emission lines, and 86 GHz continuum emission. The HII regions HII-A to HII-C in the cluster are clearly resolved into a shell-like feature with a bright-half and a dark-half in the recombination line and continuum emission. The absorption features in the molecular emission lines show that HII-A, B and C are located on the near side of the 50 km/s Molecular Cloud (50MC) but HII-D is located on the far side. The electron temperatures and densities range Te=5150-5920 K and ne=950-2340 cm-3, respectively. The electron temperatures on the bright-half are slightly lower than those on the dark-half, while the electron densities on the bright-half are slightly higher than those on the dark-half. The HII regions are located on the molecular filaments in the 50MC. They have already broken through the filaments and are growing in the surrounding molecular gas. There are some shocked molecular gas components around the HII regions. From line width of the H42a recombination line, the expansion velocities from HII-A to HII-D are estimated to be Vexp=16.7, 11.6, 11.1, and 12.1 km/s, respectively. The expansion timescales from HII-A to HII-D are estimated to be Tage~1.4x0^4, 1.7x10^4, 2.0x10^4, and 0.7x10^4 years, respectively. The spectral types of the central stars from HII-A to HII-D are estimated to be O8V, O9.5V, O9V, and B0V, respectively. The positional relation among the HII regions, the SiO molecule enhancement area, and Class-I maser spots suggest that the shock wave caused by a cloud-cloud collision propagated along the line from HII-C to HII-A in the 50MC. The shock wave would trigger the massive star formation.

arXiv comment33 pages, 13 figures, 3 tables. Accepted for publication in PASJ

References in corpus (15)

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• Cloud-cloud Collision in the Galactic Center 50 km s${}^{-1}$ Molecular Cloud
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• Properties of the Compact HII Region Complex G-0.02-0.07
• Massive Star Formation of the Sgr A East HII Regions Near the Galactic Center
• Molecular Cloud Cores in the Galactic Center 50 $\mathrm{km}{\mathrm{s}}^{-1}$ Molecular Cloud
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Cited by in corpus (5)

• PPN motion of the S-stars around Sgr A*
• The physical and chemical structure of Sagittarius B2 VIIIa. Dust and ionized gas contributions to the full molecular line survey of 47 hot cores
• ALMA Astrometry of the Objects within 0.5 pc of Sagittarius A${}^{\ast }$
• Hot Molecular Core Candidates in the Galactic Center 50 km/s Molecular Cloud
• Cloud-Cloud Collision in the Galactic Center Arc