Studies of clump structure of photodissociation regions at millimeter and sub-millimeter wavelengths

Qaiyum, Abdul; Ali, Syed Salman

doi:10.1007/bf02702313

Cited by 2 publications

(5 citation statements)

References 24 publications

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“…A study of the some of the sources have already been made by Tielens and Hollenbach (1985), Crawford et al (1985), Wolfire et al (1989), Meixner et al (1992), Meixner and Tielens (1993) and Qaiyum and Ali (2003). It can be seen from the Table 1 that the observed CII 158 μm line intensity is less than 0.3 percent of the integrated farinfrared continuum emissions, except B35 (in which case I CII /I FIR ∼ 0.0188) which is less than the maximum heating efficiency found from the Fig.…”

Section: Observationsmentioning

confidence: 79%

“…The parameters N (cm −3 ) (hydrogen density), G 0 and velocity field δ V D are varied to obtain a best fit of the observed line intensities of [CII] and [CO]. Line intensities calculated using the formalism of Qaiyum and Ali (2003) in unit of ergs, cm −2 s −1 sr −1 are presented in Table 2. The values of N (cm −3 ) and G 0 obtained for the best fit of observed values of intensities (I CII and I CO ) for 17 extragalactic and galactic sources are tabulated in columns 3 and 4 of Table 3.…”

Section: Resultsmentioning

confidence: 99%

“…It has been shown by Wolfire et al (1995), Ingalls et al (2002), Juvela et al (2003) and Qaiyum and Ali (2003) that in the cold neutral medium and translucent clouds cooling is predominantly due to 158 μm hyperfine transitions of CII ( 2 P 3/2 → 2 P 1/2 ) ( Fig. 1) while in warm neutral medium 63 μm hyperfine transition of OI ( 3 P 1 → 3 P 2 ) is found to be the most important coolant (Fig.…”

Section: Introductionmentioning

confidence: 89%

“…In the light of these observational facts the semi-infinite slab of de Jong et al (1980), extensively used in TH model, is not a safe assumption. Therefore, cooling by hyperfine transition of CI, CII, OI ,SiII and FeII and rotational transitions of CO (J → J-1) for all J up to 20 is calculated in escape probability formalism of Qaiyum and Ali (2003). The details of cooling efficiency are given in Appendix.…”

Section: Ci[307 and 609μm] Cii[158 μM] Oi[145 μM] Siii[35 μM]mentioning

confidence: 99%

“…Radiative transfer calculations are needed to obtain the estimate for Cooling by hyperfine transition of CI, CII, OI and SiII and rotational transitions of CO (J → J − 1). Escape probability formalism of Qaiyum and Ali (2003) have been used to calculate line emissions (Appendix). Photoelectric heating by dust grains is estimated using the formula of Weingartner and for average interstellar radiation field as estimated by Mezger et al (1982) and Mathis et al (1983) with total energy density =8.64 × 10 −13 erg cm −3 and =6.07 × 10 −14 erg cm −3 in the 6-13.6 eV interval.…”

Section: Introductionmentioning

confidence: 99%

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Millimeter and Submillimeter Emissions from Galactic and Extragalactic Photodissociation Regions

Qaiyum

2006

Astrophys Space Sci

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The galactic and Extragalactic photodissociation regions are primarily heated by photoelectrons ejected from the surface of interstellar dust grains by Far-ultraviolet (FUV) photons. But there is no direct mechanism to measure the photoelectric heating efficiency. To understand the role of dust grains in processing the Interstellar Radiation Field (ISRF) and heating the gas, we compare the intensities I CII , I CO and I FIR for ( 2 P 3/2 → 2 P 1/2 ) & (J = 1 → 0) line emission of CII & CO at 158 μm & 2.6 mm and integrated farinfrared from number of photodissociation regions, HII regions, planetary nebulae, reflection nebulae and high latitude translucent clouds (HLCs). It is found that I CII is linearly correlated with I FIR . In the cold medium where cloud is exposed to weak radiations temperature is low and most of the cooling is due to [CII] emissions. As a result the ratio of I CII /I FIR provide indirect method to evaluate the photoelectric heating efficiency. For the neutral cold medium it is evaluated to be ∼0.028. The FUV radiation field G 0 are estimated through the model calculation of I CII and I CO for different galactic and photodissociation regions. The intensity of FIR radiation I FIR are well represented as 1.23 × 10 −4 G 0 (ergs cm −2 s −1 sr −1 ) almost same as estimated for HLCs by Ingalls et al. (2002). Hydrogen density for each source has also been estimated.

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Section: Observationsmentioning

confidence: 79%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 89%

Section: Ci[307 and 609μm] Cii[158 μM] Oi[145 μM] Siii[35 μM]mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Millimeter and Submillimeter Emissions from Galactic and Extragalactic Photodissociation Regions

Qaiyum

2006

Astrophys Space Sci

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Integrated approach to the PDR/H ii complex by the application of carbon radio recombination lines in the millimetre range and fine-structure lines of C ii and O i

Siddiqui

Khan

Qaiyum

2020

Monthly Notices of the Royal Astronomical Society

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We have performed self-consistent calculations to estimate the physical parameters of photodissociation regions (PDRs) associated with objects, namely, NGC 2024, Orion A and W3, using far-infrared continuum emission, fine-structure lines of C ii and O i, and radio recombination lines of carbon. Typically, PDRs separate H ii regions from the molecular cloud; therefore, necessary corrections for the contribution to C ii line emission due to the H ii region are made. For that purpose, using observational data, theoretical calculations are performed to obtain the best fit for the said observations. Three parameters, angular size, θ (in arcminutes), far-ultraviolet radiation field G0, and hydrogen density nH (which gives electron density and temperature), are varied, and the sets of parameters (G0 and nH) obtained for the NGC 2024, Orion A and W3 PDRs are (7.6 × 104 and 1.2 × 105 cm−3), (2.8 × 105 and 2.3 × 105 cm−3) and (3.7 × 105 and 1.9 × 105 cm−3), respectively. The relationship between line and continuum emissions from PDRs associated with H ii regions leads us to conclude that exciting stars for the NGC 2024, Orion A and W3 H ii regions are O8–O9V, O6–O7V and O5–O6V, respectively.

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Studies of clump structure of photodissociation regions at millimeter and sub-millimeter wavelengths

Cited by 2 publications

References 24 publications

Millimeter and Submillimeter Emissions from Galactic and Extragalactic Photodissociation Regions

Millimeter and Submillimeter Emissions from Galactic and Extragalactic Photodissociation Regions

Integrated approach to the PDR/H ii complex by the application of carbon radio recombination lines in the millimetre range and fine-structure lines of C ii and O i

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