Where is OH and Does It Trace the Dark Molecular Gas (DMG)?
文献类型：期刊论文
| 作者 | 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 |
| 刊名 | ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES
 |
| 出版日期 | 2018-03-01 |
| 卷号 | 235期号:1页码:15 |
| 关键词 | evolution ISM: clouds ISM: molecules |
| ISSN号 | 0067-0049 |
| DOI | 10.3847/1538-4365/aaa762 |
| 通讯作者 | Li, Di(dili@nao.cas.cn) |
| 英文摘要 | Hydroxyl (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. |
| WOS关键词 | EMISSION-ABSORPTION OBSERVATIONS ; INTERSTELLAR DUST CLOUDS ; SENSITIVITY HI SURVEY ; CONTINUUM SOURCES ; GALACTIC OH ; LINE SURVEY ; CO ; EXCITATION ; ABUNDANCE ; HYDROXYL |
| WOS研究方向 | Astronomy & Astrophysics |
| 语种 | 英语 |
| WOS记录号 | WOS:000425654900001 |
| 出版者 | IOP PUBLISHING LTD |
| 源URL | [http://libir.pmo.ac.cn/handle/332002/22355]  |
| 专题 | 中国科学院紫金山天文台 |
| 通讯作者 | Li, Di |
| 作者单位 | 1.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 |
| 推荐引用方式 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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来源：紫金山天文台
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