Indriolo, Nick ORCID: 0000-0001-8533-6440, Neufeld, D. A., Gerin, M., Schilke, P., Benz, A. O., Winkel, B., Menten, K. M., Chambers, E. T., Black, John H., Bruderer, S., Falgarone, E., Godard, B., Goicoechea, J. R., Gupta, H., Lis, D. C., Ossenkopf, V., Persson, C. M., Sonnentrucker, P., van der Tak, F. F. S., van Dishoeck, E. F., Wolfire, Mark G. and Wyrowski, F. (2015). HERSCHEL SURVEY OF GALACTIC OH+, H2O+, AND H3O+: PROBING THE MOLECULAR HYDROGEN FRACTION AND COSMIC-RAY IONIZATION RATE. Astrophys. J., 800 (1). BRISTOL: IOP PUBLISHING LTD. ISSN 1538-4357

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Abstract

In diffuse interstellar clouds the chemistry that leads to the formation of the oxygen-bearing ions OH+, H2O+, and H3O+ begins with the ionization of atomic hydrogen by cosmic rays, and continues through subsequent hydrogen abstraction reactions involving H-2. Given these reaction pathways, the observed abundances of these molecules are useful in constraining both the total cosmic-ray ionization rate of atomic hydrogen (zeta H) and molecular hydrogen fraction (f(H2)). We present observations targeting transitions of OH+, H2O+, and H3O+ made with the Herschel Space Observatory along 20 Galactic sight lines toward bright submillimeter continuum sources. Both OH+ and H2O+ are detected in absorption in multiple velocity components along every sight line, but H3O+ is only detected along 7 sight lines. From the molecular abundances we compute f(H2) in multiple distinct components along each line of sight, and find a Gaussian distribution with mean and standard deviation 0.042 +/- 0.018. This confirms previous findings that OH+ and H2O+ primarily reside in gas with low H-2 fractions. We also infer zeta H throughout our sample, and find a lognormal distribution with mean log(zeta(H)) = -15.75 (zeta(H) = 1.78 x 10(-16) s(-1)) and standard deviation 0.29 for gas within the Galactic disk, but outside of the Galactic center. This is in good agreement with the mean and distribution of cosmic-ray ionization rates previously inferred from H-3(+) observations. Ionization rates in the Galactic center tend to be 10-100 times larger than found in the Galactic disk, also in accord with prior studies.

Item Type: Journal Article
Creators:
CreatorsEmailORCIDORCID Put Code
Indriolo, NickUNSPECIFIEDorcid.org/0000-0001-8533-6440UNSPECIFIED
Neufeld, D. A.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Gerin, M.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Schilke, P.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Benz, A. O.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Winkel, B.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Menten, K. M.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Chambers, E. T.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Black, John H.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Bruderer, S.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Falgarone, E.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Godard, B.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Goicoechea, J. R.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Gupta, H.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Lis, D. C.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Ossenkopf, V.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Persson, C. M.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Sonnentrucker, P.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
van der Tak, F. F. S.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
van Dishoeck, E. F.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Wolfire, Mark G.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Wyrowski, F.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
URN: urn:nbn:de:hbz:38-407682
DOI: 10.1088/0004-637X/800/1/40
Journal or Publication Title: Astrophys. J.
Volume: 800
Number: 1
Date: 2015
Publisher: IOP PUBLISHING LTD
Place of Publication: BRISTOL
ISSN: 1538-4357
Language: English
Faculty: Unspecified
Divisions: Unspecified
Subjects: no entry
Uncontrolled Keywords:
KeywordsLanguage
STAR-FORMING REGIONS; DIFFUSE INTERSTELLAR-MEDIUM; H I ABSORPTION; TRANSLUCENT SIGHT LINES; SIDE-BAND SPECTROSCOPY; HIGH-MASS PROTOSTARS; TRIGONOMETRIC PARALLAXES; SPIRAL ARM; PHYSICAL CONDITIONS; SAGITTARIUS B2(M)Multiple languages
Astronomy & AstrophysicsMultiple languages
URI: http://kups.ub.uni-koeln.de/id/eprint/40768

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