Hydrogen in diffuse molecular clouds in the Milky Way

Winkel, B.; Wiesemeyer, H.; Menten, K. M.; Sato, M.; Brunthaler, A.; Wyrowski, F.; Neufeld, David A.; Gérin, M.; Indriolo, Nick

doi:10.1051/0004-6361/201628597

Cited by 23 publications

(27 citation statements)

References 105 publications

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“…The presence of CH in this velocity component is not surprising, since it was known to be traced by other molecules or molecular ions like CH + (Falgarone et al 2010a), OH + and OH (Wiesemeyer et al 2016), and HF and H 2 O (Sonnentrucker et al 2015). The component consists of partially molecular, diffuse gas, since it is also present in the atomic tracers HI (Winkel et al 2017), CII (Gerin et al 2012(Gerin et al , 2015 and OI (R. Güsten, 2017, priv. comm.…”

Section: Main Characteristics Of the Observed Sightlinesmentioning

confidence: 92%

“…(c) Far-side crossing. (d) Molecular hydrogen fractions f H 2 = 2N(H 2 )/(N(HI) + 2N(H 2 )) are derived from HF (with N(HF)/N(H 2 ) = 1.4 × 10 −8 ) and from HI λ21 cm data, (Winkel et al 2017, further references therein). (e) Bayesian error estimates (accounting for the correlation between the column densities of the reported ratios).…”

Section: Chemistry Of Ch In Diffuse Gasmentioning

confidence: 99%

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Unveiling the chemistry of interstellar CH

Wiesemeyer

Güsten

Menten

et al. 2018

A&A

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Context. The methylidyne radical CH is commonly used as a proxy for molecular hydrogen in the cold, neutral phase of the interstellar medium. The optical spectroscopy of CH is limited by interstellar extinction, whereas far-infrared observations provide an integral view through the Galaxy. While the HF ground state absorption, another H2 proxy in diffuse gas, frequently suffers from saturation, CH remains transparent both in spiral-arm crossings and high-mass star forming regions, turning this light hydride into a universal surrogate for H2. However, in slow shocks and in regions dissipating turbulence its abundance is expected to be enhanced by an endothermic production path, and the idea of a “canonical” CH abundance needs to be addressed. Aim. The N = 2 ← 1 ground state transition of CH at λ149 μm has become accessible to high-resolution spectroscopy thanks to the German Receiver for Astronomy at Terahertz Frequencies (GREAT) aboard the Stratospheric Observatory for Infrared Astronomy (SOFIA). Its unsaturated absorption and the absence of emission from the star forming regions makes it an ideal candidate for the determination of column densities with a minimum of assumptions. Here we present an analysis of four sightlines towards distant Galactic star forming regions, whose hot cores emit a strong far-infrared dust continuum serving as background signal. Moreover, if combined with the sub-millimeter line of CH at λ560 μm , environments forming massive stars can be analyzed. For this we present a case study on the “proto-Trapezium” cluster W3 IRS5. Methods. While we confirm the global correlation between the column densities of HF and those of CH, both in arm and interarm regions, clear signposts of an over-abundance of CH are observed towards lower densities. However, a significant correlation between the column densities of CH and HF remains. A characterization of the hot cores in the W3 IRS5 proto-cluster and its envelope demonstrates that the sub-millimeter/far-infrared lines of CH reliably trace not only diffuse but also dense, molecular gas. Results. In diffuse gas, at lower densities a quiescent ion-neutral chemistry alone cannot account for the observed abundance of CH. Unlike the production of HF, for CH+ and CH, vortices forming in turbulent, diffuse gas may be the setting for an enhanced production path. However, CH remains a valuable tracer for molecular gas in environments reaching from diffuse clouds to sites of high-mass star formation.

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Section: Main Characteristics Of the Observed Sightlinesmentioning

confidence: 92%

Section: Chemistry Of Ch In Diffuse Gasmentioning

confidence: 99%

Unveiling the chemistry of interstellar CH

Wiesemeyer

Güsten

Menten

et al. 2018

A&A

Self Cite

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“…They were calculated by integrating the column density distributions of Winkel et al (2017) over velocity ranges equal to the median FWHM of the absorption components in this work. The H i data have an angular resolution of ∼37 (Winkel et al 2017) and the HF data used to determine the H 2 column densities ∼40 (Bergin et al 2010). The H i and H 2 column densities in the GC clouds are up to one order of magnitude higher than in the Scutum arm.…”

Section: Resultsmentioning

confidence: 99%

“…3). The column densities of H i and H 2 in the diffuse clouds are shown in the panels of methanol (Winkel et al 2017). The values for H i, H 2 , the hot core, and the protostellar envelope are scaled by the factor given in parentheses.…”

Section: Discussionmentioning

confidence: 99%

Complex organic molecules in diffuse clouds along the line of sight to Sagittarius B2

Thiel

Беллоче

Menten

et al. 2017

A&A

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Context. Up to now, mostly relatively simple molecules have been detected in interstellar diffuse molecular clouds in our galaxy, but more complex species have been reported in the diffuse/translucent medium of a z = 0.89 spiral galaxy. Aims. We aim at searching for complex organic molecules (COMs) in diffuse molecular clouds along the line of sight to Sgr B2(N), taking advantage of the high sensitivity and angular resolution of the Atacama Large Millimeter/submillimeter Array (ALMA). Methods. We use data acquired as part of the EMoCA survey performed with ALMA. To analyse the absorption features of the molecules detected towards the ultracompact H ii region K4 in Sgr B2(N), we calculate synthetic spectra for these molecules and fit their column densities, line widths, centroid velocities, and excitation temperatures. Results. We report the detection of CH 3 OH, CH 3 CN, CH 3 CHO, HC 3 N, and NH 2 CHO in Galactic center (GC) diffuse clouds and CH 3 OH and CH 3 CN in a diffuse cloud in the Scutum arm. The chemical composition of one of the diffuse GC clouds is found to be similar to the one of the diffuse/translucent medium of the z = 0.89 spiral galaxy. Conclusions. The chemical processes leading to chemical complexity in the diffuse molecular ISM appear to have remained similar since z = 0.89. As proposed in previous studies, the presence of COMs in diffuse molecular clouds may result from a cyclical interstellar process of cloud contraction and expansion between diffuse and dense states.

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“…In Milky Way, a large neutral hydrogen column density N(H I) is in general associated with H 2 (Savage et al 1977;Winkel et al 2017;Marasco et al 2017). If the physical conditions of high-z galaxies are similar to that of Milky Way, it is expected that large N(H I) regions at high-z galaxies are also associated with H 2 .…”

Section: Introductionmentioning

confidence: 99%

Physical conditions in two high-redshift H2-bearing GRB-DLAs, 120815A and 121024A

Shaw

Ferland

2020

Monthly Notices of the Royal Astronomical Society

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The gamma-ray burst (GRB) afterglows provide an unique opportunity to study the interstellar medium (ISM) of star-forming galaxies at high-redshift. The GRB-DLAs (damped Lyman-α absorbers) contain a large neutral hydrogen column density, N(H I), and are observed against the GRB afterglow. A large fraction of GRB-DLAs show presence of molecular hydrogen (H 2 ) which is an indicator of star-formation. Hence it is important to study those GRB-DLAs which have H 2 lines to decipher and understand their physical conditions. The GRB-DLAs 121024A and 120815A, situated at redshift 2.30 and 2.36 respectively, are two such important H 2 -bearing GRB-DLAs. Besides H 2 , these two GRB-DLAs also show many metal lines. In this work we have carried out a detail numerical study on the H 2 lines, as well as on those metal lines, in GRB-DLAs 121024A and 120815A self-consistently. We use the spectral synthesis code CLOUDY for this study. This modeling helps us to determine the underlying physical conditions which give rise such lines and hence to understand these two GRB-DLAs in much more detail than any other previous investigation. We find that the hydrogen densities for these two H 2 -bearing DLAs are ≥ 60 cm −3 . Moreover our study infers that the linear sizes are ≤ 17.7 pc for these two GRB-DLAs, and the mean gas temperatures averaged over the cloud thickness, are ≤ 140 K. Overall, we find that these two H 2 -bearing GRB-DLAs are denser, cooler and smaller compared to those without H 2 .

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Hydrogen in diffuse molecular clouds in the Milky Way

Cited by 23 publications

References 105 publications

Unveiling the chemistry of interstellar CH

Unveiling the chemistry of interstellar CH

Complex organic molecules in diffuse clouds along the line of sight to Sagittarius B2

Physical conditions in two high-redshift H2-bearing GRB-DLAs, 120815A and 121024A

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