Line emission from spherical UV irradiated clumps

Störzer, H.; Køster, Brian; Stutzki, J.; Sternberg, A.

doi:10.1007/bfb0102131

Cited by 105 publications

(169 citation statements)

References 2 publications

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“…In an earlier paper (Röllig et al 2012) we presented early Stratospheric Observatory For Infrared Astronomy (SOFIA, Young et al 2012) observations of the [C II] 158 µm fine-structure transition of C + at 1900.536900 GHz and the 12 CO(11−10) transition at 1496.922909 GHz at two GMCs in the central molecular ring of IC 342. Using KOSMA-τ PDR model calculations (Störzer et al 1996;Röllig et al 2006Röllig et al , 2013 we were able to distinguish between a strong PDR/star-burst emission in the southern GMC E and the much more quiescent conditions in the cooler and denser GMC C in the northern arm, confirming the findings of Meier & Turner (2005).…”

Section: Introductionsupporting

confidence: 77%

[C II] 158μm and [N II] 205μm emission from IC 342

Röllig

Simon

Güsten

et al. 2016

A&A

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Context. Atomic fine-structure line emission is a major cooling process in the interstellar medium (ISM). In particular the [C II] 158 µm line is one of the dominant cooling lines in photon-dominated regions (PDRs). However, it is not confined to PDRs but can also originate from the ionized gas closely surrounding young massive stars. observed with the GREAT receiver on board SOFIA.We present different methods to utilize the superior spatial and spectral resolution of our new data to infer information on how the gas kinematics in the nuclear region influence the observed line profiles. In particular we present a super-resolution method to derive how unresolved, kinematically correlated structures in the beam contribute to the observed line shapes. Results. We find that the emission coming from the ionized gas shows a kinematic component in addition to the general Doppler signature of the molecular gas. We interpret this as the signature of two bi-polar lobes of ionized gas expanding out of the galactic plane. We then show how this requires an adaptation of our understanding of the geometrical structure of the nucleus of IC 342. Examining the starburst activity we find ratios I([C II])/I( 12 CO(1−0)) between 400 and 1800 in energy units. Applying predictions from numerical models of H II and PDR regions to derive the contribution from the ionized phase to the total [C II] emission we find that 35−90% of the observed [C II] intensity stems from the ionized gas if both phases contribute. Averaged over the central few hundred parsec we find for the [C II] contribution a H II-to-PDR ratio of 70:30. Conclusions. The ionized gas in the center of IC 342 contributes more strongly to the overall [C II] emission than is commonly observed on larger scales and than is predicted. Kinematic analysis shows that the majority of the [C II] emission is related to the strong but embedded star formation in the nuclear molecular ring and only marginally emitted from the expanding bi-polar lobes of ionized gas.

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Section: Introductionsupporting

confidence: 77%

[C II] 158μm and [N II] 205μm emission from IC 342

Röllig

Simon

Güsten

et al. 2016

A&A

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“…2). The line width of the CH + 2-1 and 1-0 transitions is not only significantly larger than the width of dense gas tracers, but also of species that trace a similar region to CH + , such as CO + (Störzer et al 1995;Fuente et al 2003). The 5 km s −1 is comparable to the width of tracers of the interclump medium, such as C + (Δv ∼ 3.8 km s −1 , also shown in Fig.…”

Section: Resultsmentioning

confidence: 79%

“…The CO + peak (α J2000 = 05 h 35 m 20.6 s , δ J2000 = −05 • 25 14 ) in the Orion Bar (Störzer et al 1995) has been observed as part of the Herschel observations of EXtra-Ordinary Sources (HEXOS) guaranteed-time key program (Bergin et al 2010) for the Heterodyne Instrument for the Far-Infrared (HIFI, De Graauw et al 2010) of the Herschel Space Observatory (Pilbratt et al 2010) in every HIFI band as a spectral scan. The data were reduced using the Herschel interactive processing environment (HIPE, Ott et al 2010) pipeline version 6.0.…”

Section: Observations and Data Reductionmentioning

confidence: 99%

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

Nagy

Tak

Ossenkopf

et al. 2013

A&A

203

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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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“…We use the KOSMA-τ PDR code (Störzer et al 1996;Röllig et al 2006) 2 to numerically solve the coupled equations of energy balance (heating and cooling), chemical equilibrium, and radiative transfer. The main features of the KOSMA-τ PDR model are: a) spherical model symmetry, i.e finite model clouds; b) modular chemistry, which means, that chemical species can easily be added or removed from the network and the network will rebuild dynamically; c) isotope chemistry including 13 C and 18 O; and d) optimization toward large model grids in parameter space, allowing for example to build up any composition of individual clouds in order to simulate clumpy material (for details see Cubick et al 2008).…”

Section: The Kosma-τ Pdr Modelmentioning

confidence: 99%

Carbon fractionation in photo-dissociation regions

Röllig

Ossenkopf

2013

A&A

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We upgraded the chemical network from the UMIST Database for Astrochemistry 2006 to include isotopes such as 13 C and 18 O. This includes all corresponding isotopologues, their chemical reactions and the properly scaled reaction rate coefficients. We study the fractionation behavior of astrochemically relevant species over a wide range of model parameters, relevant for modelling of photo-dissociation regions (PDRs). We separately analyze the fractionation of the local abundances, fractionation of the total column densities, and fractionation visible in the emission line ratios. We find that strong C + fractionation is possible in cool C + gas. Optical thickness as well as excitation effects produce intensity ratios between 40 and 400. The fractionation of CO in PDRs is significantly different from the diffuse interstellar medium. PDR model results never show a fractionation ratio of the CO column density larger than the elemental ratio. Isotope-selective photo-dissociation is always dominated by the isotope-selective chemistry in dense PDR gas. The fractionation of C, CH, CH + and HCO + is studied in detail, showing that the fractionation of C, CH and CH + is dominated by the fractionation of their parental species. The light hydrides chemically derive from C + , and, consequently, their fractionation state is coupled to that of C + . The fractionation of C is a mixed case depending on whether formation from CO or HCO + dominates. Ratios of the emission lines of [C ii], [C i], 13 CO, and H 13 CO + provide individual diagnostics to the fractionation status of C + , C, and CO.

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Line emission from spherical UV irradiated clumps

Cited by 105 publications

References 2 publications

[C II] 158μm and [N II] 205μm emission from IC 342

[C II] 158μm and [N II] 205μm emission from IC 342

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

Carbon fractionation in photo-dissociation regions

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Line emission from spherical UV irradiated clumps

Cited by 105 publications

References 2 publications

[C II] 158μm and [N II] 205μm emission from IC 342

[C II] 158μm and [N II] 205μm emission from IC 342

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

Carbon fractionation in photo-dissociation regions

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