Interstellar H<sub>3</sub><sup>+</sup>Line Absorption toward LkHα 101

Brittain, S.; Simon, Theodore; Kulesa, Craig; Rettig, T. W.

doi:10.1086/383024

Cited by 21 publications

(27 citation statements)

References 34 publications

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“…) in dense clouds (Geballe & Oka 1996;McCall et al 1999;Brittain et al 2004) and diffuse clouds ( McCall et al 1998aGeballe et al 1999). Contrary to the expectation from chemical model calculations, which predict orders of magnitude lower H þ 3 number density for diffuse clouds ( because of rapid dissociative recombination with electrons), our observations have established that column densities of H Oka 2004b).…”

Section: à2contrasting

confidence: 98%

“…It is difficult to determine the number and natures of the lower velocity warm clouds that contribute to the trough, because of their weak absorptions and the contamination by strong and narrow spectral features. However, some of the absorption is certainly due to the aforementioned 20 km s À1 cloud, and it seems probable that the remainder also is located inside the CMZ; the high velocity spread is in sharp contrast to that of H þ 3 in many cold dense and diffuse clouds in the Galactic disk, which always give narrow lines (Geballe & Oka 1996;Geballe et al 1999;McCall et al 1998aMcCall et al , 1999McCall et al , 2002McCall et al , 2003Brittain et al 2004). Observations of many more sources distributed over a wider region of the CMZ under high spectroscopic resolution will be attempted in the near future to obtain a more detailed picture of those clouds.…”

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confidence: 99%

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Hot and Diffuse Clouds near the Galactic Center Probed by Metastable \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\t

Oka

Geballe

Goto

et al. 2005

ApJ

185

149

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Using an absorption line from the metastable (J ; K) ¼ (3; 3) level of H þ 3 together with other lines of H þ 3 and CO observed along several sight lines, we have discovered a vast amount of high-temperature (T $ 250 K) and lowdensity (n $ 100 cm À3 ) gas with a large velocity dispersion in the central molecular zone (CMZ) of the Galaxy, i.e., within 200 pc of the center. Approximately three-fourths of the H þ 3 along the line of sight to the brightest source we observed, the Quintuplet object GCS 3-2, is inferred to be in the CMZ, with the remaining H , is probably closer to the center. CO is not very abundant in these clouds. Hot and diffuse gas in which the (3, 3) level is populated was not detected toward several dense clouds and diffuse clouds in the Galactic disk where large column densities of colder H þ 3 have been reported previously. Thus, the newly discovered environment appears to be unique to the CMZ. The large observed H þ 3 column densities in the CMZ suggest an ionization rate much higher than in the diffuse interstellar medium in the Galactic disk. Our finding that the H þ 3 in the CMZ is almost entirely in diffuse clouds indicates that the reported volume filling factor ( f ! 0:1) for n ! 10 4 cm À3 clouds in the CMZ is an overestimate by at least an order of magnitude.

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Section: à2contrasting

confidence: 98%

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confidence: 99%

Hot and Diffuse Clouds near the Galactic Center Probed by Metastable \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\t

Oka

Geballe

Goto

et al. 2005

ApJ

185

149

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“…The images were cleaned of hot and dead pixels as well as cosmic-ray hits and were then resampled spectrally and spatially so that the resulting images placed spectral and spatial dimensions orthogonally, falling along rows and columns, respectively. Details of our reduction and analysis techniques can be found in Brittain et al (2003Brittain et al ( , 2004. The observations began with the NIRSPEC entrance slit in a position angle of 15 and finished with a position angle of 45…”

Section: Observationsmentioning

confidence: 99%

CO Emission and Absorption toward V1647 Orionis (McNeil’s Nebula)

Rettig¹,

Brittain²,

Gibb³

et al. 2005

ApJ

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We present high-resolution infrared spectra of V1647 Ori, the illuminating star of McNeil's Nebula, which reveal the presence of hot and cold gas-phase CO and ices of CO and H 2 O. The emission lines of 12 CO (1-0), (2-1), and (3-2) likely originate from $2500 K gas in an inner accretion disk region, where substantial clearing of dust has occurred. The width of the emission lines increases with increasing J-value, suggesting that the hottest CO gas we detect is located closest to the central star. The narrower widths of the low-J CO emission lines are indicative of more distant, cooler material in the inner disk. Superposed on the low-J emission lines are narrow 12 CO absorption components, which are typical of cold interstellar cloud material at a temperature of $18 K. The very low column density and very cold temperature for the absorbing gas suggest that we are viewing the central star through intervening material within the L1630 cloud and that the disk is oriented nearly face-on. The Doppler shift of the cold CO is offset from the hot gas by 6 AE 2 km s À1 , so it is likely that the very cold CO originates in a foreground cloud rather than the circumstellar material surrounding V1647 Ori. Model fits to the strong H 2 O and CO ice absorption bands are consistent with cold (<20 K) amorphous water ice ( ¼ 0:65) and predominantly apolar CO ice ( ¼ 0:58). The CO and H 2 O ices are unprocessed (unannealed), similar to the ices in dense clouds.

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“…H + 3 has been observed in a variety of environments: dense clouds (Geballe & Oka 1996;McCall et al 1999;Brittain et al 2004;Gibb et al 2010), diffuse clouds (McCall et al 1998;Geballe et al 1999;McCall et al 2002McCall et al , 2003Indriolo et al 2007;Indriolo & McCall 2012) and even the nucleus of an extragalactic source (Geballe et al 2006). A comprehensive review has been recently published (Oka 2013).…”

Section: Introductionmentioning

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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Interstellar H₃⁺Line Absorption toward LkHα 101

Abstract: We present a detection of three lines of the H þ 3 ion in the near-infrared spectrum of the Herbig Be star LkH 101.

Cited by 21 publications

References 34 publications

CO Emission and Absorption toward V1647 Orionis (McNeil’s Nebula)

Physical conditions in the central molecular zone inferred by H₃⁺

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Interstellar H3+Line Absorption toward LkHα 101

Abstract: We present a detection of three lines of the H þ 3 ion in the near-infrared spectrum of the Herbig Be star LkH 101.

Cited by 21 publications

References 34 publications

CO Emission and Absorption toward V1647 Orionis (McNeil’s Nebula)

Physical conditions in the central molecular zone inferred by H3+

Contact Info

Product

Resources

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Interstellar H₃⁺Line Absorption toward LkHα 101

Physical conditions in the central molecular zone inferred by H₃⁺