The influence of continuum radiation fields on hydrogen radio recombination lines

Prozesky, Andri; Smits, Derck P.

doi:10.1093/mnras/sty1189

Cited by 10 publications

(31 citation statements)

References 43 publications

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“…In the range of principal quantum number n=20 to 160 and at the condition of T=10000 K and n e =10000 cm −3 , the average deviation between our values and those of Storey & Hummers (1995) is 0.29%. And compared with those of Prozesky & Smits (2018), it is 2.0%. The largest discrepancies are 0.79% and 4.7% compared with Storey & Hummers (1995) and Prozesky & Smits (2018), respectively.…”

Section: Line Intensity Ratiosmentioning

confidence: 87%

“…The more sophisticated nl-model including angular momentum changing collisions was used in Storey & Hummers (1995). Recently, Prozesky & Smits (2018) presented new results using nl-model with new numerical techniques to ensure convergence of the solution and updated calculations about radiative and collisional transitions, and the effects on departure coefficients of continuum radiation are also considered.…”

Section: Line Intensity Ratiosmentioning

confidence: 99%

“…The stopping criterion suggested in Prozesky & Smits (2018) is not used, and we terminate the iterative procedure if the largest difference of b m between two iterations is less than 1.0 × 10 −6 . The radiation field could also affect the level populations, but this effect become noticeable only if n e > 10 4 cm −3 (Prozesky & Smits 2018). This condition is not satisfied by the H II region models simulated in the current work.…”

Section: Line Intensity Ratiosmentioning

confidence: 99%

“…So the effect of radiation field is neglected in our algorithm. In order to assess the reliability of the algorithm to calculate departure coefficients, the results given by Storey & Hummers (1995) and Prozesky & Smits (2018) are compared with ours. The comparison is presented in Figure 1.…”

Section: Line Intensity Ratiosmentioning

confidence: 99%

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Determining Electron Temperature and Density in a H ii Region Using the Relative Strengths of Hydrogen Radio Recombination Lines

Zhu

Wang

et al. 2019

ApJ

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We have introduced a new method of estimating the electron temperature and density of H II regions by using single dish observations. In this method, multiple hydrogen radio recombination lines of different bands are computed under the assumption of low optical depth. We use evolutionary hydrodynamical models of H II regions to model hydrogen recombination line emission from a variety of H II regions and assess the reliability of the method. According to the simulated results, the error of the estimated temperature is commonly < 13%, and that of the estimated density is < 25% for a < 1% uncertainty of the observed line fluxes. A reasonable estimated value of electron density can be achieved if the uncertainty of the line fluxes are lower than 3%. In addition, the estimated values are more representative of the properties in the relatively high-density region if the gas density gradient is present in the H II region. Our method can be independent of the radio continuum observations. But the accuracy will be improved if a line-to-continuum ratio at millimeter wavelengths is added to the estimation. Our method provides a way to measure the temperature and density in ionized regions without interferometers.

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Section: Line Intensity Ratiosmentioning

confidence: 87%

Section: Line Intensity Ratiosmentioning

confidence: 99%

Section: Line Intensity Ratiosmentioning

confidence: 99%

Section: Line Intensity Ratiosmentioning

confidence: 99%

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Determining Electron Temperature and Density in a H ii Region Using the Relative Strengths of Hydrogen Radio Recombination Lines

Zhu

Wang

et al. 2019

ApJ

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“…A capture-collision-cascade (C 3 ) model, such as the one described by Prozesky & Smits (2018) (hereafter PS18), accounts for the influence that radiation has on atoms in an astronomical cloud by solving the statistical balance equations (SBE) for the level populations of hydrogen. This type of model is appropriate when the plasma is optically thin.…”

Section: Challenges Of Maser Modelingmentioning

confidence: 99%

An nl-model with radiative transfer for hydrogen recombination line masers

Prozesky

Smits

2019

Monthly Notices of the Royal Astronomical Society

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Atomic hydrogen masers occur in recombination plasmas in sufficiently dense H ii regions. These hydrogen recombination line (HRL) masers have been observed in a handful of objects to date and the analysis of the atomic physics involved has been rudimentary. In this work a new model of HRL masers is presented which uses an nlmodel to describe the atomic populations interacting with free-free radiation from the plasma, and an escape probability framework to deal with radiative transfer effects. The importance of including the collisions between angular momentum quantum states and the free-free emission in models of HRL masers is demonstrated. The model is used to describe the general behaviour of radiative transfer of HRLs and to investigate the conditions under which HRL masers form. The model results show good agreement with observations collected over a broad range of frequencies. Theoretical predictions are made regarding the ratio of recombination lines from the same upper quantum level for these objects.

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Carbon radio recombination lines from gigahertz to megahertz frequencies towards Orion A

Salas

Oonk

Emig

et al. 2019

A&A

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Context. The combined use of carbon radio recombination lines (CRRLs) and the 158 µm- [CII] line is a powerful tool for the study of the energetics and physical conditions (e.g., temperature and density) of photodissociation regions (PDRs). However, there are few observational studies that exploit this synergy. Aims. Here we explore the relation between CRRLs and the 158 µm-[CII] line in light of new observations and models. Methods. We present new and existing observations of CRRLs in the frequency range 0.15-230 GHz with ALMA, VLA, the GBT, Effelsberg 100m, and LOFAR towards Orion A (M42). We complement these observations with SOFIA observations of the 158 µm-[CII] line. We studied two PDRs: the foreground atomic gas, known as the Veil, and the dense PDR between the HII region and the background molecular cloud.Results. In the Veil we are able to determine the gas temperature and electron density, which we use to measure the ionization parameter and the photoelectric heating efficiency. In the dense PDR, we are able to identify a layered PDR structure at the surface of the molecular cloud to the south of the Trapezium cluster. There we find that the radio lines trace the colder portion of the ionized carbon layer, the C + /C/CO interface. By modeling the emission of the 158 µm-[CII] line and CRRLs as arising from a PDR we derive a thermal pressure > 5 × 10 7 K cm −3 and a radiation field G0 ≈ 10 5 close to the Trapezium. Conclusions. This work provides additional observational support for the use of CRRLs and the 158 µm-[CII] line as complementary tools to study dense and diffuse PDRs, and highlights the usefulness of CRRLs as probes of the C + /C/CO interface.

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The influence of continuum radiation fields on hydrogen radio recombination lines

Cited by 10 publications

References 43 publications

Determining Electron Temperature and Density in a H ii Region Using the Relative Strengths of Hydrogen Radio Recombination Lines

Determining Electron Temperature and Density in a H ii Region Using the Relative Strengths of Hydrogen Radio Recombination Lines

An nl-model with radiative transfer for hydrogen recombination line masers

Carbon radio recombination lines from gigahertz to megahertz frequencies towards Orion A

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