Widespread Rotationally Hot Hydronium Ion in the Galactic Interstellar Medium

Lis, D. C.; Schilke, P.; Bergin, Edwin A.; Gérin, M.; Black, J. H.; Comito, C.; Luca, Massimo De; Godard, B.; Higgins, R.; Petit, Franck; Pearson, John C.; Pellegrini, E.; Phillips, T. G.; Yu, Shanshan

doi:10.1088/0004-637x/785/2/135

Cited by 29 publications

(39 citation statements)

References 46 publications

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“…Herschel observations of H 3 O + line absorption over long sightlines toward Sgr B2 and W 31C revealed surprisingly large amounts of the ion in highly excited rotational energy levels (E rot /k ∼ 1000 K above the ground state). These rotationally "hot" molecules do not require molecular gas at high kinetic temperature (≥ 400 K) because the exoergic formation process H 2 O + + H 2 → H 3 O + + H converts the chemical energy difference between reactants and products into internal (rotational) energy of H 3 O + (Lis et al 2014). In this interpretation, the observations place rather direct constraints on the chemical source rate of H 3 O + , and they imply CR ionization rates that are in harmony with the rates deduced from OH + , H 2 O + , and H + 3 both in the Galactic disk and in the CMZ.…”

Section: Observations Of Molecular Ions: Hmentioning

confidence: 99%

The Nine Lives of Cosmic Rays in Galaxies

Grenier

Black

Strong

2015

Annu. Rev. Astron. Astrophys.

317

294

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Cosmic-ray astrophysics has advanced rapidly in recent years, and its impact on other astronomical disciplines has broadened. Many new experiments, measuring the particles both directly in the atmosphere or space, and indirectly via γ rays and synchrotron radiation, have widened the range and quality of the information available on their origin, propagation, and interactions. The impact of low-energy cosmic rays on interstellar chemistry is a fast-developing topic, including the propagation of these particles into the clouds where the chemistry occurs. Cosmic rays, via their γ-ray production, also provide a powerful way to probe the gas content of the interstellar medium. Substantial advances have been made in the observations and modelling of the interplay between cosmic rays and the interstellar medium. Focussing on energies up to 1 TeV, these inter-relating aspects are covered at various levels of detail, giving a guide to the state of the subject. CONTENTS

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Section: Observations Of Molecular Ions: Hmentioning

confidence: 99%

The Nine Lives of Cosmic Rays in Galaxies

Grenier

Black

Strong

2015

Annu. Rev. Astron. Astrophys.

317

294

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“…Formation pumping has also been discussed as an explanation for the observed excitation of H 3 O + (e.g. Lis et al 2014;González-Alfonso et al 2013), and may be important for other molecular ions as described further in Section 4 below.…”

Section: Ltementioning

confidence: 99%

“…In the case of high-lying metastable states, however, the effects of "formation pumping" may complicate the interpretation of the observations (e.g. Lis et al 2014). The Zeeman splitting of hydride spectral lines offers another important diagnostic tool that has been used to estimate the interstellar magnetic field strength.…”

Section: Other Diagnostic Usesmentioning

confidence: 99%

Interstellar Hydrides

Gérin

Neufeld

Goicoechea

2016

Annu. Rev. Astron. Astrophys.

129

171

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Interstellar hydrides -that is, molecules containing a single heavy element atom with one or more hydrogen atoms -were among the first molecules detected outside the solar system. They lie at the root of interstellar chemistry, being among the first species to form in initially-atomic gas, along with molecular hydrogen and its associated ions. Because the chemical pathways leading to the formation of interstellar hydrides are relatively simple, the analysis of the observed abundances is relatively straightforward and provides key information about the environments where hydrides are found. Recent years have seen rapid progress in our understanding of interstellar hydrides, thanks largely to far-IR and submillimeter observations performed with the Herschel Space Observatory. In this review, we will discuss observations of interstellar hydrides, along with the advanced modeling approaches that have been used to interpret them, and the unique information that has thereby been obtained.

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“…Schilke et al (2010Schilke et al ( , 2013) report the detection of the H 2 O + ion toward Sgr B2 with Herschel, whereas Lis et al (2012Lis et al ( , 2014 report H 3 O + detection. Indriolo et al (2015) derive their column densities in the different velocity components.…”

Section: Additional Constraints: Ohmentioning

confidence: 99%

Physical conditions in the central molecular zone inferred by H₃⁺

Petit¹,

Ruaud²,

Bron³

et al. 2016

A&A

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Context. The H + 3 molecule has been detected in many lines of sight within the central molecular zone (CMZ) with exceptionally large column densities and unusual excitation properties compared to diffuse local clouds. The detection of the (3, 3) metastable level has been suggested to be the signature of warm and diffuse gas in the CMZ. Aims. We aim to determine the physical conditions and processes in the CMZ that explain the ubiquitous properties of H + 3 in this medium and to constrain the value of the cosmic-ray ionization rate. Methods. We use the Meudon photodissociation region (PDR) code in which H + 3 excitation has been implemented. We re-examine the relationship between the column density of H + 3 and the cosmic-ray ionization rate, ζ, up to large values of ζ in the frame of this full chemical model. We study the impact of the various mechanisms that can excite H + 3 in its metastable state. We produce grids of PDR models exploring different parameters (ζ, size of clouds, metallicity) and infer the physical conditions that best match the observations toward ten lines of sight in the CMZ. For one of them, Herschel observations of HF, OH + , H 2 O + , and H 3 O + can be used as additional constraints. We check that the results found for H + 3 also account for the observations of these molecules. Results. We find that the linear relationship between N(H + 3 ) and ζ only holds up to a certain value of the cosmic-ray ionization rate, which depends on the proton density. A value ζ ∼ 1−11 × 10 −14 s −1 explains both the large observed H + 3 column density and its excitation in the metastable level (3, 3). This ζ value agrees with that derived from synchrotron emission and Fe Kα line. It also reproduces N(OH + ), N(H 2 O + ) and N(H 3 O + ) detected toward Sgr B2(N). We confirm that the CMZ probed by H + 3 is diffuse, n H 100 cm −3 and warm, T ∼ 212−505 K. This warm medium is due to cosmic-ray heating. We also find that the diffuse component probed by H + 3 must fill a large fraction of the CMZ. Finally, we suggest the warm gas in the CMZ enables efficient H 2 formation via chemisorption sites as in PDRs. This contributes to enhance the abundance of H + 3 in this high cosmic-ray flux environment.

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Widespread Rotationally Hot Hydronium Ion in the Galactic Interstellar Medium

Cited by 29 publications

References 46 publications

The Nine Lives of Cosmic Rays in Galaxies

The Nine Lives of Cosmic Rays in Galaxies

Interstellar Hydrides

Physical conditions in the central molecular zone inferred by H₃⁺

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Widespread Rotationally Hot Hydronium Ion in the Galactic Interstellar Medium

Cited by 29 publications

References 46 publications

The Nine Lives of Cosmic Rays in Galaxies

The Nine Lives of Cosmic Rays in Galaxies

Interstellar Hydrides

Physical conditions in the central molecular zone inferred by H3+

Contact Info

Product

Resources

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Physical conditions in the central molecular zone inferred by H₃⁺