Molecular clouds and galactic spiral structure
Molecular clouds and galactic spiral structure
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DOI：
10.1086/183290
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发表时间：
1980-07
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影响因子：
--
通讯作者：
R. Cohen;H. Cong;T. Dame;P. Thaddeus
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文献类型：
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作者：
R. Cohen;H. Cong;T. Dame;P. Thaddeus
对银道面进行的两次大规模2.6毫米CO巡天，一次在第一象限（l=12/sup 0/至60/sup 0/，B=-1/sup 0/至+1/sup 0/），另一个在第二个（l=105/sup 0/至139/sup 0/，B=-3/sup 0/至+3/sup 0/）提供的证据表明，与以前的发现相反，分子云构成了螺旋结构的高度特异性示踪物。在经典的21厘米螺旋臂中，有五个的分子对应物已经被确认：英仙座臂、本旋臂（包括林德布拉德的本旋膨胀环）、人马座臂、盾牌座臂和4千秒差距臂。本旋臂和英仙座臂之间的区域显然没有分子云，而银河系内部的臂间区域似乎基本上没有分子云。CO螺旋结构意味着分子云的平均寿命不可能超过1 x 10/sup 8/年，这是星际物质穿过螺旋臂所需的时间。质量守恒对星际介质中以分子云形式存在的部分设定了限制：在距离银河系中心4- 12 kpc的任何距离上，它都不可能超过一半。
Two large-scale 2.6 mm CO surveys of the galactic plane, one in the first quadrant (l=12/sup 0/ to 60/sup 0/, b=-1/sup 0/ to +1/sup 0/), the other in the second (l=105/sup 0/ to 139/sup 0/, b=-3/sup 0/ to +3/sup 0/), have provided evidence that, contrary to previous findings, molecular clouds constitute a highly specific tracer of spiral structure. Molecular counterparts of five of the classical 21 cm spiral arms have been identified: the Perseus arm, the local arm (including Lindblad's local expanding ring), the Sagittarius arm, the Scutum arm, and the 4-kpc arm. The region between the local arm and the Perseus arm is apparently devoid of molecular clouds, and the interarm regions of the inner Galaxy appear largely so. CO spiral structure implies that the mean lifetime of molecular clouds cannot be greater than 1 x 10/sup 8/ years, the time required for interstellar matter to cross a spiral arm. Conservation of mass then sets a limit on the fraction of the interstellar medium in the form of molecular clouds: it cannot exceed one-half at any distance from the galactic center in the range 4--12 kpc.