G28.17+0.05: An Unusual Giant H I Cloud in the Inner Galaxy
G28.17+0.05: An Unusual Giant H I Cloud in the Inner Galaxy
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G28.17 0.05：内星系中不寻常的巨大H I云
DOI：
10.1086/321500
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发表时间：
2001
期刊：
影响因子：
--
通讯作者：
Jennifer A. Lockman
中科院分区：
文献类型：
--
作者：
A. Minter;F. J. Lockman;G. Langston;Jennifer A. Lockman
新的21 cm H I观测揭示了银河系平面中具有不寻常性质的巨大H I云。它的定义相当明确，在5千秒差距的距离上，直径约为150秒差距，包含多达105兆焦耳的原子氢。云的外部出现在H I背景之上的H I发射，而中心区域显示H I自吸收。重现观测结果的模型有一个温度为140 K的核心和一个高达一个数量级的外壳。冷核沿着银道面沿着拉长，而星云的整体轮廓近似为球形。H I云的温暖和寒冷的部分有相似的和相对较大的线宽，~7 km s-1。云核是一个源弱，被动激发1720 MHz OH发射，也有一个相对较大的线宽，划定的H I自吸收区域，但速度略有蓝移。1720 MHz的OH发射的强度与NH来自模型的冷芯。有12 CO排放与云核心。大部分云质量是分子，总质量大于2 × 105 M。在冷芯中，H1质量分数可以是~ 10%。星云中只有少数几个星星形成的地方。在银河系内部可能还有大约100个这样的天体;在银河系中心50°以内通过银河系平面的每一条视线都可能至少与一个相交。我们认为，G28.17+0.05是一个云被观察到，因为它进入一个螺旋臂，它是在从原子到分子状态的过渡。
New 21 cm H I observations have revealed a giant H I cloud in the Galactic plane that has unusual properties. It is quite well defined, about 150 pc in diameter at a distance of 5 kpc, and contains as much as 105 M☉ of atomic hydrogen. The outer parts of the cloud appear in H I emission above the H I background, while the central regions show H I self-absorption. Models that reproduce the observations have a core with a temperature ≲40 K and an outer envelope as much as an order of magnitude hotter. The cold core is elongated along the Galactic plane, whereas the overall outline of the cloud is approximately spherical. The warm and cold parts of the H I cloud have similar and relatively large line widths, ~7 km s-1. The cloud core is a source of weak, anomalously excited 1720 MHz OH emission, also with a relatively large line width, which delineates the region of H I self-absorption but is slightly blueshifted in velocity. The intensity of the 1720 MHz OH emission is correlated with NH derived from models of the cold core. There is 12CO emission associated with the cloud core. Most of the cloud mass is in molecules, and the total mass is greater than 2 × 105 M☉. In the cold core the H I mass fraction may be ~10%. The cloud has only a few sites of current star formation. There may be ~100 more objects like this in the inner Galaxy; every line of sight through the Galactic plane within 50° of the Galactic center probably intersects at least one. We suggest that G28.17+0.05 is a cloud being observed as it enters a spiral arm and that it is in the transition from the atomic to the molecular state.
影响因子：
8.7
作者：
LOCKMAN, FJ
通讯作者：
LOCKMAN, FJ