Broad Radio Recombination Lines from Hypercompact H<scp>ii</scp>Regions

Sewiło, M.; Churchwell, E.; Kurtz, S.; Goss, W. M.; Höfner, P.

doi:10.1086/382268

Cited by 129 publications

(168 citation statements)

References 59 publications

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“…Located at a distance of ∼3.3 kpc (Kuchar & Bania 1994), G34 has been widely studied in radio continuum (Turner et al 1974;Reid & Ho 1985;Wood & Churchwell 1989;Sewiło et al 2011) and radio recombination lines (Garay et al 1985(Garay et al , 1986Gaume et al 1994;Sewiło et al 2004Sewiło et al , 2011. Several components have been identified in radio continuum observations: two ultra compact HII regions called A and B, a more evolved HII region with a cometary shape (component C), and an extended (1 ) HII region (component D) in the south-east.…”

Section: Source Descriptionmentioning

confidence: 99%

Water deuterium fractionation in the high-mass star-forming region G34.26+0.15 based on Herschel/HIFI data

Coutens

Vastel

Hincelin

et al. 2014

Monthly Notices of the Royal Astronomical Society

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Understanding water deuterium fractionation is important for constraining the mechanisms of water formation in interstellar clouds. Observations of HDO and H 18 2 O transitions were carried out towards the high-mass star-forming region G34.26+0.15 with the HIFI instrument onboard the Herschel Space Observatory, as well as with ground-based single-dish telescopes. Ten HDO lines and three H 18 2 O lines covering a broad range of upper energy levels (22-204 K) were detected. We used a non-LTE 1D analysis to determine the HDO/H 2 O ratio as a function of radius in the envelope. Models with different water abundance distributions were considered in order to reproduce the observed line profiles. The HDO/H 2 O ratio is found to be lower in the hot core (∼3.5 × 10 −4 -7.5 × 10 −4 ) than in the colder envelope (∼1.0 × 10 −3 -2.2 × 10 −3 ). This is the first time that a radial variation of the HDO/H 2 O ratio has been found to occur in a high-mass source. The chemical evolution of this source was modeled as a function of its radius and the observations are relatively well reproduced. The comparison between the chemical model and the observations leads to an age of ∼10 5 years after the infrared dark cloud stage.

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Section: Source Descriptionmentioning

confidence: 99%

Water deuterium fractionation in the high-mass star-forming region G34.26+0.15 based on Herschel/HIFI data

Coutens

Vastel

Hincelin

et al. 2014

Monthly Notices of the Royal Astronomical Society

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“…Note.-Electron density, n e , required to produce the observed increase in the width of the centimeter RRL over the millimeter RRL by pressure broadening. a Keto 2002. b Sewilo et al 2004. c Garay et al 1986.…”

Section: The Correlation Of Line Widths Velocities and Frequenciesmentioning

confidence: 99%

“…It is unclear how high the densities might be, because the density cannot be reliably determined from the radio continuum if the gas is optically thick. Second, when observed at centimeter wavelengths, these small H ii regions often show very broad radio recombination line (RRL) widths, more than 3 or 4 times the thermal line width (Altenhoff et al 1981;Zijlstra et al 1990;Afflerbach et al 1994;DePree et al 1994DePree et al , 1995DePree et al , 1996DePree et al , 1997Gaume et al 1995b;Keto et al 1995;Johnson et al 1998;Jaffe & Martín-Pintado 1999;Keto 2002;Sewilo et al 2004;Keto & Wood 2006). Not all the small H ii regions have this property, but those that do are sometimes referred to as broad recombination line objects.…”

Section: Introductionmentioning

confidence: 99%

The Early Evolution of Massive Stars: Radio Recombination Line Spectra

Keto

Zhang

Kurtz

2008

ApJ

106

122

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Velocity shifts and differential broadening of radio recombination lines are used to estimate the densities and velocities of the ionized gas in several hypercompact and ultracompact H ii regions. These small H ii regions are thought to be at their earliest evolutionary phase and associated with the youngest massive stars. The observations suggest that these H ii regions are characterized by high densities, supersonic flows, and steep density gradients, consistent with accretion and outflows that would be associated with the formation of massive stars.

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“…This method is called the H i emission/absorption (H i E/A) method (Kuchar & Bania 1994;Kolpak et al 2003;Anderson & Bania 2009;Urquhart et al 2012) and it relies on the detection of H i absorption at 21 cm from the continuum emission of an H ii region. A similar method uses intervening H 2 CO clouds instead of H i to search for an absorption signal (Wilson 1972;Downes et al 1980;Araya et al 2002;Watson et al 2003;Sewilo et al 2004). Because there is less H 2 CO compared to H i, this method will more often resolve the KDA incorrectly and is applicable to a smaller number of H ii regions.…”

Section: Introductionmentioning

confidence: 99%

The Green Bank Telescope H Ii Region Discovery Survey. Iii. Kinematic Distances

Bania

Balser

Rood

2012

ApJ

101

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Using the H i emission/absorption method, we resolve the kinematic distance ambiguity and derive distances for 149 of 182 (82%) H ii regions discovered by the Green Bank Telescope H ii Region Discovery Survey (GBT HRDS). The HRDS is an X-band (9 GHz, 3 cm) GBT survey of 448 previously unknown H ii regions in radio recombination line and radio continuum emission. Here, we focus on HRDS sources from 67• , where kinematic distances are more reliable. The 25 HRDS sources in this zone that have negative recombination line velocities are unambiguously beyond the orbit of the Sun, up to 20 kpc distant. They are the most distant H ii regions yet discovered. We find that 61% of HRDS sources are located at the far distance, 31% at the tangent-point distance, and only 7% at the near distance. "Bubble" H ii regions are not preferentially located at the near distance (as was assumed previously) but average 10 kpc from the Sun. The HRDS nebulae, when combined with a large sample of H ii regions with previously known distances, show evidence of spiral structure in two circular arc segments of mean Galactocentric radii of 4.25 and 6.0 kpc. We perform a thorough uncertainty analysis to analyze the effect of using different rotation curves, streaming motions, and a change to the solar circular rotation speed. The median distance uncertainty for our sample of H ii regions is only 0.5 kpc, or 5%. This is significantly less than the median difference between the near and far kinematic distances, 6 kpc. The basic Galactic structure results are unchanged after considering these sources of uncertainty.

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Broad Radio Recombination Lines from Hypercompact HiiRegions

Cited by 129 publications

References 59 publications

Water deuterium fractionation in the high-mass star-forming region G34.26+0.15 based on Herschel/HIFI data

Water deuterium fractionation in the high-mass star-forming region G34.26+0.15 based on Herschel/HIFI data

The Early Evolution of Massive Stars: Radio Recombination Line Spectra

The Green Bank Telescope H Ii Region Discovery Survey. Iii. Kinematic Distances

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