A theoretical study of the radio recombination line and continuum emission from compact inhomogeneous H II regions

1979 ◽  
Vol 39 ◽  
pp. 405 ◽  
Author(s):  
M. R. Viner ◽  
J. P. Vallee ◽  
V. A. Hughes
Keyword(s):  
Theoretical Study ◽  
Continuum Emission ◽  
H Ii Regions ◽  
Recombination Line ◽  
Radio Recombination Line

Metallicity Structure across the Galactic Disk: Radio Observations of H ii Regions

2017 ◽  
Vol 13 (S334) ◽  
pp. 275-276
Author(s):  
Dana S. Balser ◽  
Trey V. Wenger ◽  
T. M. Bania ◽  
L. D. Anderson
Keyword(s):  
Electron Temperature ◽  
Massive Star ◽  
Galactic Disk ◽  
Radio Continuum ◽  
Continuum Emission ◽  
H Ii Regions ◽  
Thermal Electron ◽  
Radio Recombination Line ◽  
Nuclear Processing ◽  
Metallicity Distribution

AbstractHii regions are the sites of massive star formation and are the archetypal tracers of spiral arms. Because of their short lifetimes (<10 Myr) their abundances provide a measure of the nuclear processing of many stellar generations. Here we review our ongoing efforts to explore the metallicity structure of the Galactic disk by observing radio recombination line (RRL) and thermal radio continuum emission toward Hii regions. The RRL-to-continuum ratio provides an accurate measure of the electron temperature which is used as a proxy for metallicity. Since collisionally excited lines from metals (e.g., O, C) are the main coolant in Hii regions, the thermal electron temperature is well correlated with metallicity (e.g., [O/H]). We determine Hii region distances from maser parallax measurements when possible; otherwise we use kinematic distances. Such radio diagnostics of Hii regions yield an extinction free tracer to map the metallicity distribution across the entire Galactic disk.

A hydrogen and helium radio recombination-line survey of galactic H II regions at 10 GHz

1979 ◽  
Vol 229 ◽  
pp. 524 ◽  
Author(s):  
S. M. Lichten ◽  
L. F. Rodriguez ◽  
E. J. Chaisson
Keyword(s):  
H Ii Regions ◽  
Recombination Line ◽  
Radio Recombination Line ◽  
Line Survey

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

2019 ◽  
Vol 71 (6) ◽  
Author(s):  
Masato Tsuboi ◽  
Yoshimi Kitamura ◽  
Kenta Uehara ◽  
Atsushi Miyazaki ◽  
Ryosuke Miyawaki ◽  
...  
Keyword(s):  
Shock Wave ◽  
Galactic Center ◽  
Emission Lines ◽  
Continuum Emission ◽  
Molecular Gas ◽  
H Ii Regions ◽  
Recombination Line ◽  
The Galaxy ◽  
H Ii Region ◽  
Absorption Features

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 recombination line, the expansion velocities of HII-A, HII-B, HII-C, and HII-D are estimated to be Vexp = 16.7, 11.6, 11.1, and 12.1 km s−1, respectively. The expansion timescales of HII-A, HII-B, HII-C, and HII-D are estimated to be tage ≃ 1.4 × 104, 1.7 × 104, 2.0 × 104, and 0.7 × 104 yr, 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. These derived spectral types are roughly consistent with the previous radio estimation. The positional relation among the H ii regions, the SiO molecule enhancement area, and Class-I maser spots suggest that a 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 have triggered the massive star formation.

scholarly journals Radio continuum and radio recombination line observations of the Galactic center lobe

2013 ◽  
Vol 9 (S303) ◽  
pp. 129-131
Author(s):  
Halca Nagoshi ◽  
Kenta Fujisawa ◽  
Yuzo Kubose
Keyword(s):  
Electron Temperature ◽  
Galactic Center ◽  
Thermal Emission ◽  
Radio Continuum ◽  
Continuum Emission ◽  
Recombination Line ◽  
Ionized Gas ◽  
Radio Recombination Line ◽  
Spatial Coverage ◽  
The Continuum

AbstractRadio continuum (cont) and radio recombination line (RRL) observations with the Yamaguchi 32-m radio telescope toward the lower part of the Galactic center lobe (GCL) in the Galactic center region are presented. While two ridges of the GCL were seen in both continuum and RRL images, the spatial coverage of the ridges of the continuum and RRL is not coincident. We distinguish the continuum emission of the GCL into thermal and non-thermal emission by assuming an electron temperature of the ionized gas of 4370 K, estimated based on the line width (14.1 km s−1). The thermal emission was found to be located inside and surrounded by the non-thermal emission.

scholarly journals The evolution of young HII regions

2018 ◽  
Vol 611 ◽  
pp. A99 ◽  
Author(s):  
P. D. Klaassen ◽  
K. G. Johnston ◽  
J. S. Urquhart ◽  
J. C. Mottram ◽  
T. Peters ◽  
...  
Keyword(s):  
High Mass ◽  
Continuum Emission ◽  
Molecular Gas ◽  
Recombination Line ◽  
Low Mass Stars ◽  
Velocity Gradients ◽  
Radio Recombination Line ◽  
Low Mass ◽  
The Relationship ◽  
Initial Results

Context. High-mass stars form in much richer environments than those associated with isolated low-mass stars, and once they reach a certain mass, produce ionised (HII) regions. The formation of these pockets of ionised gas are unique to the formation of high-mass stars (M > 8 M⊙), and present an excellent opportunity to study the final stages of accretion, which could include accretion through the HII region itself. Aim. This study of the dynamics of the gas on both sides of these ionisation boundaries in very young HII regions aims to quantify the relationship between the HII regions and their immediate environments. Methods. We present high-resolution (~0.5″) ALMA observations of nine HII regions selected from the red MSX source survey with compact radio emission and bolometric luminosities greater than 104 L⊙. We focus on the initial presentation of the data, including initial results from the radio recombination line H29α, some complementary molecules, and the 256 GHz continuum emission. Results. Of the six (out of nine) regions with H29α detections, two appear to have cometary morphologies with velocity gradients across them, and two appear more spherical with velocity gradients suggestive of infalling ionised gas. The remaining two were either observed at low resolution or had signals that were too weak to draw robust conclusions. We also present a description of the interactions between the ionised and molecular gas (as traced by CS (J = 5 − 4)), often (but not always) finding the HII region had cleared its immediate vicinity of molecules. Conclusions. Of our sample of nine, the observations of the two clusters expected to have the youngest HII regions (from previous radio observations) are suggestive of having infalling motions in the H29α emission, which could be indicative of late stage accretion onto the stars despite the presence of an HII region.

scholarly journals The Galactic center lobe filled with thermal plasma

2019 ◽  
Vol 71 (4) ◽  
Author(s):  
Halca Nagoshi ◽  
Yuzo Kubose ◽  
Kenta Fujisawa ◽  
Kazuo Sorai ◽  
Yoshinori Yonekura ◽  
...  
Keyword(s):  
Thermal Plasma ◽  
Galactic Center ◽  
Galactic Plane ◽  
Radio Continuum ◽  
Continuum Emission ◽  
Galactic Rotation ◽  
Observational Result ◽  
Recombination Line ◽  
The North ◽  
Radio Recombination Line

Abstract An observational result of a radio continuum and H92α radio recombination line of the Galactic center lobe (GCL), using the Yamaguchi 32 m radio telescope, is reported. The obtained spatial intensity distribution of the radio recombination line shows two distinctive ridge-like structures extending from the Galactic plane vertically to the north at the eastern and western sides of the Galactic center, which are connected to each other at a latitude of ${1{^{\circ}_{.}}2}$ to form a loop-like structure as a whole. This suggests that most of the radio continuum emission of the GCL is free–free emission, and that the GCL is filled with thermal plasma. The east ridge of the GCL observed with the radio recombination line separates 30 pc from the radio arc, which has been considered a part of the GCL, but coincides with a ridge of the radio continuum at a Galactic longitude of 0°. The radial velocity of the radio recombination line is found to be between −4 and +10 km s−1 across the GCL. This velocity is much smaller than expected from the Galactic rotation, and hence indicates that the GCL exists apart from the Galactic center. These characteristics of the GCL suggest that the long-standing hypothesis that the GCL was created by explosive activity in the Galactic center is unlikely, but favor that the GCL is a giant H ii region.

scholarly journals New detections of (sub)millimeter hydrogen radio recombination lines towards high-mass star-forming clumps

2018 ◽  
Vol 616 ◽  
pp. A107 ◽  
Author(s):  
W.-J. Kim ◽  
J. S. Urquhart ◽  
F. Wyrowski ◽  
K. M. Menten ◽  
T. Csengeri
Keyword(s):  
High Velocity ◽  
Radio Continuum ◽  
High Mass ◽  
Continuum Emission ◽  
Photon Flux ◽  
Mass Star ◽  
Recombination Line ◽  
Lyman Continuum ◽  
Radio Recombination Line ◽  
5 Ghz

Aims. Previous radio recombination line (RRL) observations of dust clumps identified in the APEX Telescope Large Area Survey of the Galaxy (ATLASGAL) have led to the detection of a large number of RRLs in the 3 mm range. Here, we aim to study their excitation with shorter wavelength (sub)millimeter radio recombination line (submm-RRL) observations. Methods. We made observations of submm-RRLs with low principal quantum numbers (n ≤ 30) using the APEX 12 m telescope, toward 104 H II regions associated with massive dust clumps from ATLASGAL. The observations covered the H25α, H28α, and H35β transitions. Toward a small subsample the H26α, H27α, H29α, and H30α lines were observed to avoid contamination by molecular lines at adjacent frequencies. Results. We have detected submm-RRLs (signal-to-noise (S∕N)≥ 3 σ) from compact H II regions embedded within 93 clumps. The submm-RRLs are approximately a factor of two brighter than the mm-RRLs and consistent with optically thin emission in local thermodynamic equilibrium (LTE). The average ratio (0.31) of the measured H35β/H28α fluxes is close to the LTE value of 0.28. No indication of RRL maser emission has been found. The Lyman photon flux, bolometric, and submm-RRL luminosities toward the submm-RRL detected sources present significant correlations. The trends of dust temperature and the ratio of bolometric luminosity to clump mass, Lbol ∕Mclump, indicate that the H II regions are related to the most massive and luminous clumps. By estimating the production rate of ionizing photons, Q, from the submm-RRL flux, we find that the Q(H28α) measurements provide estimates of the Lyman continuum photon flux consistent with those determined from 5 GHz radio continuum emission. Six RRL sources show line profiles that are a combination of a narrow and a broad Gaussian feature. The broad features are likely associated with high-velocity ionized flows. Conclusions. We have detected submm-RRLs toward 93 ATLASGAL clumps. Six RRL sources have high-velocity RRL components likely driven by high-velocity ionized flows. Their observed properties are consistent with thermal emission that correlates well with the Lyman continuum flux of the H II regions. The sample of H II regions with mm/submm-RRL detections probes, in our Galaxy, luminous clumps (Lbol > 104 L⊙) with high Lbol∕Mclump. We also provide suitable candidates for further studies of the morphology and kinematics of embedded, compact H II regions with the Atacama Large Millimeter/submillimeter Array (ALMA).

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