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Where is OH and Does It Trace the Dark Molecular Gas (DMG)?
Li, Di1,2,3; Tang, Ningyu1; Nguyen, Hiep4,5,6; Dawson, J. R.4,5,6; Heiles, Carl7; Xu, Duo1,3,8; Pan, Zhichen1; Goldsmith, Paul F.9; Gibson, Steven J.10; Murray, Claire E.11,12; Robishaw, Tim13; McClure-Griffiths, N. M.14; Dickey, John15; Pineda, Jorge9; Stanimirovic, Snezana11; Bronfman, L.16; Troland, Thomas17
2018-03-01
Source PublicationASTROPHYSICAL JOURNAL SUPPLEMENT SERIES
ISSN0067-0049
Volume235Issue:1Pages:15
Corresponding AuthorLi, Di(dili@nao.cas.cn)
AbstractHydroxyl (OH) is expected to be abundant in diffuse interstellar molecular gas because it forms along with H-2 under similar conditions and forms within a similar extinction range. We have analyzed absorption measurements of OH at 1665 MHz and 1667 MHz toward 44 extragalactic continuum sources, together with the J = 1-0 transitions of (CO)-C-12, (CO)-C-13, and (CO)-O-18, and the J = 2-1 transition of (CO)-C-12. The excitation temperatures of OH were found to follow a modified lognormal distribution f(T-ex) proportional to 1/root 2 pi sigma exp [-[ln(T-ex) - ln(3.4 K)(2)]/2 sigma(2)], the peak of which is close to the temperature of the Galactic emission background (CMB+ synchrotron). In fact, 90% of the OH has excitation temperatures within 2 K of the Galactic background at the same location, providing a plausible explanation for the apparent difficulty of mapping this abundant molecule in emission. The opacities of OH were found to be small and to peak around 0.01. For gas at intermediate extinctions (A(V) similar to 0.05-2 mag), the detection rate of OH with a detection limit N(OH) similar or equal to 10(12) cm(-2) is approximately independent of A(V). We conclude that OH is abundant in the diffuse molecular gas and OH absorption is a good tracer of "dark molecular gas (DMG)." The measured fraction of DMG depends on the assumed detection threshold of the CO data set. The next generation of highly sensitive low-frequency radio telescopes, such as FAST and SKA, will make feasible the systematic inventory of diffuse molecular gas through decomposing, in velocity, the molecular (e.g., OH and CH) absorption profiles toward background continuum sources with numbers exceeding what is currently available by orders of magnitude.
Keywordevolution ISM: clouds ISM: molecules
DOI10.3847/1538-4365/aaa762
WOS KeywordEMISSION-ABSORPTION OBSERVATIONS ; INTERSTELLAR DUST CLOUDS ; SENSITIVITY HI SURVEY ; CONTINUUM SOURCES ; GALACTIC OH ; LINE SURVEY ; CO ; EXCITATION ; ABUNDANCE ; HYDROXYL
Indexed BySCI
Language英语
WOS Research AreaAstronomy & Astrophysics
WOS SubjectAstronomy & Astrophysics
WOS IDWOS:000425654900001
PublisherIOP PUBLISHING LTD
Citation statistics
Cited Times:6[WOS]   [WOS Record]     [Related Records in WOS]
Document Type期刊论文
Identifierhttp://libir.pmo.ac.cn/handle/332002/22356
Collection中国科学院紫金山天文台
Corresponding AuthorLi, Di
Affiliation1.Chinese Acad Sci, Natl Astron Observ, Beijing 100012, Peoples R China
2.Chinese Acad Sci, Key Lab Radio Astron, Nanjing, Jiangsu, Peoples R China
3.Univ Chinese Acad Sci, Beijing 100049, Peoples R China
4.Macquarie Univ, Dept Phys & Astron, Sydney, NSW 2109, Australia
5.Macquarie Univ, MQ Res Ctr Astron Astrophys & Astrophoton, Sydney, NSW 2109, Australia
6.CSIRO Astron & Space Sci, Australia Telescope Natl Facil, POB 76, Epping, NSW 1710, Australia
7.Univ Calif Berkeley, Dept Astron, 601 Campbell Hall 3411, Berkeley, CA 94720 USA
8.Univ Texas Austin, Dept Astron, RLM 15308, Austin, TX 78712 USA
9.CALTECH, Jet Prop Lab, 4800 Oak Grove Dr, Pasadena, CA 91109 USA
10.Western Kentucky Univ, Dept Phys & Astron, 1906 Coll Hts Blvd, Bowling Green, KY 42101 USA
11.Univ Wisconsin, Dept Astron, 475 N Charter St, Madison, WI 53706 USA
12.Space Telescope Sci Inst, 3700 San Martin Dr, Baltimore, MD 21218 USA
13.Natl Res Council Canada, Dominion Radio Astrophys Observ, POB 248, Penticton, BC V2A 6J9, Canada
14.Australian Natl Univ, Res Sch Astron & Astrophys, Canberra, ACT 2611, Australia
15.Univ Tasmania, Sch Maths & Phys, Hobart, Tas 7001, Australia
16.Univ Chile, Dept Astron, Casilla 36, Santiago, Chile
17.Univ Kentucky, Dept Phys & Astron, Lexington, KY 40506 USA
Recommended Citation
GB/T 7714
Li, Di,Tang, Ningyu,Nguyen, Hiep,et al. Where is OH and Does It Trace the Dark Molecular Gas (DMG)?[J]. ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES,2018,235(1):15.
APA Li, Di.,Tang, Ningyu.,Nguyen, Hiep.,Dawson, J. R..,Heiles, Carl.,...&Troland, Thomas.(2018).Where is OH and Does It Trace the Dark Molecular Gas (DMG)?.ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES,235(1),15.
MLA Li, Di,et al."Where is OH and Does It Trace the Dark Molecular Gas (DMG)?".ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES 235.1(2018):15.
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