Comparative study of CH<sup>+</sup>and SH<sup>+</sup>absorption lines observed towards distant star-forming regions

Godard, B.; Falgarone, É.; Gérin, M.; Lis, D. C.; Luca, Massimo De; Black, J. H.; Goicoechea, J. R.; Cernicharo, J.; Neufeld, David A.; Menten, K. M.; Emprechtinger, M.

doi:10.1051/0004-6361/201117664

Cited by 138 publications

(208 citation statements)

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“…For low-density diffuse interstellar clouds, C-shocks (Pineau des Forêts et al 1986) and turbulent dissipation (Godard et al 2009) have been proposed and confirmed by Falgarone et al (2010a,b) and Godard et al (2012). Alternatively, in denser regions with strong far-ultraviolet (FUV) radiation fields, the internal energy available in the vibrationally excited H 2 molecules A&A 550, A96 (2013) has been proposed to help overcome the large activation barrier (Sternberg & Dalgarno 1995;Agundez et al 2010).…”

Section: Introductionmentioning

confidence: 86%

“…Menten et al 2011) and properties of turbulent dissipation regions (e.g. Godard et al 2012), in clouds exposed to high UV irradiation these abundances are sensitive to the abundance ratios of H, H 2 , and electrons as a function of depth into the cloud, which are determined by the radiation field strength of the irradiation source.…”

Section: The Destruction Of Ch + and Sh +mentioning

confidence: 99%

“…After nondetections of SH + in the UV domain in the spectra of nearby stars (Millar & Hobbs 1988;Magnani & Salzer 1989, 1991, the 526 GHz N J = 1 2 −0 1 transition of SH + has been detected in emission using Herschel toward the high-mass protostar W3 IRS 5 . The 526 GHz transition has also been detected in absorption in the diffuse interstellar medium towards various distant star-forming regions (Godard et al 2012). The 683 GHz transition of SH + has been detected in absorption towards Sgr B2(M) from the ground with the Carbon Heterodyne Array of the MPIfR (CHAMP+) receiver of the Atacama Pathfinder Experiment 12 m telescope (APEX; Menten et al 2011).…”

Section: Introductionmentioning

confidence: 99%

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The chemistry of ions in the Orion Bar I. – CH⁺, SH⁺, and CF⁺

Nagy

Tak

Ossenkopf

et al. 2013

A&A

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Context. The abundances of interstellar CH + and SH + are not well understood as their most likely formation channels are highly endothermic. Several mechanisms have been proposed to overcome the high activation barriers, including shocks, turbulence, and H 2 vibrational excitation. Aims. Using data from the Herschel Space Observatory, we studied the formation of ions, in particular CH + and SH + in a typical high UV-illumination warm and dense photon-dominated region (PDR), the Orion Bar. Methods. The HIFI instrument on board Herschel provides velocity-resolved line profiles of CH + 1-0 and 2-1 and three hyperfine transitions of SH + 1 2 −0 1 . The PACS instrument provides information on the excitation and spatial distribution of CH + by extending the observed CH + transitions up to J = 6-5. We compared the observed line intensities to the predictions of radiative transfer and PDR codes. Results. All CH + , SH + , and CF + lines analyzed in this paper are seen in emission. The widths of the CH + 2-1 and 1-0 transitions are of ∼5 km s −1 , significantly broader than the typical width of dense gas tracers in the Orion Bar (∼2-3 km s −1 ) and are comparable to the width of species that trace the interclump medium such as C + and HF. The detected SH + transitions are narrower compared to CH + and have line widths of ∼3 km s −1 , indicating that SH + emission mainly originates in denser condensations. Non-LTE radiative transfer models show that electron collisions affect the excitation of CH + and SH + and that reactive collisions need to be taken into account to calculate the excitation of CH + . Comparison to PDR models shows that CH + and SH + are tracers of the warm surface region (A V < 1.5) of the PDR with temperatures between 500 and 1000 K. We have also detected the 5-4 transition of CF + at a width of ∼1.9 km s −1 , consistent with the width of dense gas tracers. The intensity of the CF + 5-4 transition is consistent with previous observations of lower-J transitions toward the Orion Bar.Conclusions. An analytic approximation and a numerical comparison to PDR models indicate that the internal vibrational energy of H 2 can explain the formation of CH + for typical physical conditions in the Orion Bar near the ionization front. The formation of SH + is also likely to be explained by H 2 vibrational excitation. The abundance ratios of CH + and SH + trace the destruction paths of these ions, and indirectly, the ratios of H, H 2 , and electron abundances as a function of depth into the cloud.

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Section: Introductionmentioning

confidence: 86%

Section: The Destruction Of Ch + and Sh +mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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The chemistry of ions in the Orion Bar I. – CH⁺, SH⁺, and CF⁺

Nagy

Tak

Ossenkopf

et al. 2013

A&A

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203

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“…Therefore, their reaction products will be formed at detectable abundance if the corresponding reaction endothermicity is overcome by turbulent dissipation, shocks, or shears. Submillimeter absorptions from both the neutral SH, that is, the mercapto radical, and the sulfanylium (SH + ) have been observed in foreground diffuse molecular clouds toward star-forming regions (Menten et al 2011;Godard et al 2012;Neufeld et al 2012Neufeld et al , 2015. Consequently, the analysis of sulfur hydrides provides unique physical and chemical constraints on models that are applied to the interstellar medium.…”

Section: Introductionmentioning

confidence: 99%

“…Consequently, the analysis of sulfur hydrides provides unique physical and chemical constraints on models that are applied to the interstellar medium. In particular, SH + has been suggested as an important probe of turbulence in the diffuse ISM (Godard et al 2012(Godard et al , 2014.…”

Section: Introductionmentioning

confidence: 99%

Mercapto radical (SH) in translucent interstellar clouds

Zhao

Галазутдинов

Linnartz

et al. 2015

A&A

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We present the first detection of rotationally resolved electronic transitions of the mercapto radical (SH) in the near-ultraviolet in translucent interstellar clouds. Observational data acquired by the Ultraviolet and Visual Echelle Spectrograph of the Very Large Telescope were used to search for the near-ultraviolet absorption spectra of SH. Two weak absorption features at ∼3242.40 and 3240.66 Å, assigned as the p P 11 (3/2) and the ( q P 21 (3/2) + q Q 11 (3/2)) doublet transitions in the A 2 Σ + -X 2 Π (0, 0) band of SH, respectively, were identified in the averaged spectrum of four selected lines of sight: HD 73882, HD 78344, HD 80077, and HD 154368. These features are weak, but can be identified within a 3σ detection limit, and are found in other published data sets as well. We compiled a set of line positions and oscillator strengths of SH to facilitate the data analysis. We derived an averaged value of the SH column density, ∼1.5 ± 0.3 × 10 13 cm −2 , that is most likely representative for the magnitude of SH column densities in individual SH-rich translucent clouds. This value is also consistent with predictions from models for C-type shocks and turbulent dissipation regions with typical translucent cloud conditions.

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