G−0.02−0.07, the compact H ii region complex nearest to the galactic center with ALMA
Abstract

We have observed the compact H ii region complex nearest to the dynamical center of the Galaxy, G−0.02−0.07, using ALMA in the H42α recombination line, CS J = 2–1, H13CO+J = 1–0, and SiO v = 0, J = 2–1 emission lines, and the 86 GHz continuum emission. The H ii 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 analysis of the absorption features in the molecular emission lines show that H ii-A, B, and C are located on the near side of the “Galactic center 50 km s−1 molecular cloud” (50MC), but HII-D is located on the far side of it. The electron temperatures and densities ranges are Te = 5150–5920 K and ne = 950–2340 cm−3, respectively. The electron temperatures in the bright half are slightly lower than those in the dark half, while the electron densities in the bright half are slightly higher than those in the dark half. The H ii regions are embedded in the ambient molecular gas. There are some molecular gas components compressed by a C-type shock wave around the H ii regions. From the line width of the H42α more »

Authors:
;  ;  ;  ;  ;  ;
Publication Date:
NSF-PAR ID:
10124744
Journal Name:
Publications of the Astronomical Society of Japan
Volume:
71
Issue:
6
ISSN:
0004-6264
Publisher:
Oxford University Press
4. ABSTRACT We report Keck–NIRSPEC observations of the Brackett α 4.05 μm recombination line across the two candidate embedded super star clusters (SSCs) in NGC 1569. These SSCs power a bright H ii region and have been previously detected as radio and mid-infrared sources. Supplemented with high-resolution VLA mapping of the radio continuum along with IRTF–TEXES spectroscopy of the [S iv] 10.5 μm line, the Brackett α data provide new insight into the dynamical state of gas ionized by these forming massive clusters. Near-infrared sources detected in 2 μm images from the slit-viewing Camera are matched with Gaia sources to obtain accurate celestial coordinates and slit positions to within ∼0${_{.}^{\prime\prime}}$1. Br α is detected as a strong emission peak powered by the less luminous infrared source, MIR1 (LIR ∼ 2 × 107 $\rm L_\odot$). The second candidate SSC MIR2 is more luminous (LIR ≳ 4 × 108 $\rm L_\odot$) but exhibits weak radio continuum and Br α emission, suggesting the ionized gas is extremely dense (ne ≳ 105 cm−3), corresponding to hypercompact H ii regions around newborn massive stars. The Br α and [S iv] lines across the region are both remarkably symmetric and extremely narrow, with observed line widths Δv ≃ 40 $\rm km\, s^{-1}$, full width at half-maximum. This result is the first clear evidence thatmore »