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题名: (CO)-C-12, (CO)-C-13 and (CO)-O-18 observations along the major axes of nearby bright infrared galaxies
作者: Tan, Qing-Hua1, 2, 3; Gao Yu(高煜)1; Zhang, Zhi-Yu1, 2; Xia, Xiao-Yang3
刊名: RESEARCH IN ASTRONOMY AND ASTROPHYSICS
出版日期: 2011-07-01
卷号: 11, 期号:7, 页码:787-810
关键词: galaxies: ISM ; ISM: clouds ; ISM: molecules ; radio lines: ISM
文章类型: Article
英文摘要: We present simultaneous observations of (CO)-C-12, (CO)-C-13 and (CO)-O-18 J=1-0 emission in 11 nearby (cz <1000 km s(-1)) bright infrared galaxies. Both (CO)-C-12 and (CO)-C-13 are detected in the centers of all the galaxies, except for (CO)-C-13 in NGC 3031. We have also detected (CO)-O-18, CSJ=2-1 and HCO+ J=1-0 emission in the nuclear regions of M82 and M51. These are the first systematical extragalactic detections of (CO)-C-12 and its isotopes from the PMO 14 m telescope. We have conducted half-beam-spaced mapping of M82 over an area of 4' x 2.5' and major axis mapping of NGC 3627, NGC 3628, NGC 4631 and M51. The radial distributions of (CO)-C-12 and (CO)-C-13 in NGC 3627, NGC 3628 and M51 can be well fitted by an exponential profile. The (CO)-C-12/(CO)-C-13 intensity ratio, R, decreases monotonically with the galactocentric radius in all mapped sources. The average R in the center and disk of the galaxies are 9.9 +/- 3.0 and 5.6 +/- 1.9, respectively, much lower than the peculiar R(similar to 24) found in the center of M82. The intensity ratios of (CO)-C-13/(CO)-O-18, (CO)-C-13/HCO+ and (CO)-C-13/CS (either our or literature data) show little variation with galactocentric radius, in sharp contrast with the greatly varied R. This supports the notion that the observed gradient in R could be the result of the variations of the physical conditions across the disks. The H-2 column density derived from (CO)-O-18 shows that the Galactic standard conversion factor (X-factor) overestimates the amount of the molecular gas in M82 by a factor of similar to 2.5. These Observations suggest that the X-factor in active star-forming regions (i.e., nuclear regions) should be lower than that in normal star-forming disks and the gradient in R can be used to trace the variations of the X-factor.
WOS标题词: Science & Technology ; Physical Sciences
类目[WOS]: Astronomy & Astrophysics
研究领域[WOS]: Astronomy & Astrophysics
关键词[WOS]: DENSE MOLECULAR GAS ; STAR-FORMATION ; SPIRAL GALAXIES ; CARBON-MONOXIDE ; CO SURVEY ; ULTRALUMINOUS GALAXIES ; PHYSICAL CONDITIONS ; IRREGULAR GALAXIES ; GALACTIC-CENTER ; COLUMN DENSITY
收录类别: SCI
语种: 英语
WOS记录号: WOS:000293037500005
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内容类型: 期刊论文
URI标识: http://libir.pmo.ac.cn/handle/332002/15976
Appears in Collections:期刊(老文献)_期刊论文

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作者单位: 1.Chinese Acad Sci, Purple Mt Observ, Nanjing 210008, Peoples R China
2.Chinese Acad Sci, Grad Sch, Beijing 100039, Peoples R China
3.Tianjin Normal Univ, Tianjin Astrophys Ctr, Tianjin 300384, Peoples R China
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