Giant molecular clouds in the galaxy: The distribution of /sup 13/CO emission in the galactic plane
Giant molecular clouds in the galaxy: The distribution of /sup 13/CO emission in the galactic plane
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星系中的巨型分子云：/sup 13/CO 排放在银道面的分布
DOI：
10.1086/183042
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发表时间：
1979
期刊：
影响因子：
--
通讯作者：
N. Scoville
中科院分区：
文献类型：
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作者：
P. Solomon;D. B. Sanders;N. Scoville
本文报道了银河赤道1 ≤ 44/sup 0/的一氧化碳同位素（/sup 13/CO）的观测结果。由于/sup 13/CO线预计有低的不透明度（τ approx.1），它们的强度变化作为银河系半径的函数更容易解释的气体密度变化比饱和，近热化/sup 12/CO线。在R=4 ~ 8 kpc处，/sup 13/CO的发射率随银河半径的变化呈现出一个峰值，与以前报道的/sup 12/CO的峰值几乎相同。J（/sup 12/CO）/J（/sup 13/CO）=5.5 ± 0.63。三角洲在3<或=R<或=9 kpc的范围内，R=0.5 kpc的间隔。因此，我们验证了存在一个高密度的巨大的分子云环中间的太阳和银河系中心。在这个结构中，氢分子的密度是同一区域氢原子密度的10倍。气体的典型柱密度通过这个环在lapprox.30/sup 0/观测到的（H/sub 2/）是4 × 10/sup 22/ cm/sup-2/或A/sub v/approx.40 mag.这些结果验证了使用/sup 12/CO线观测来绘制更多的分子气体分布的星系图，因为/sup 13/CO和/sup 12/CO发射率在银河系尺度上显示出相似的变化。这两条线在光学深度上有很大差异，它们的分布相似，表明在银道面上的/sup 12/CO线积分强度主要是云的数量的量度，并且在银道面H/sub 2/的大部分区域的温度相当相似（T/sub k/approx.10 K）。在R=4和R=8 kpc之间，/sup 12/CO//sup 13/CO发射率比的变化小于40%，尽管它与误差范围内的恒定同位素丰度比一致。«少
A survey of the carbon monoxide isotope (/sup 13/CO) is reported for the galactic equator at l< or =44/sup 0/. Since the /sup 13/CO lines are expected to have low opacity (tauapprox.1), their intensity variations as a function of galactic radius are more readily interpreted in terms of gas density variations than are the saturated, nearly thermalized /sup 12/CO lines. The distribution of /sup 13/CO emissivity as a function of galactic radius shows a peak at R=4 to 8 kpc nearly identical to that previously reported for /sup 12/CO. J (/sup 12/CO)/J (/sup 13/CO) =5.5 +- 0.63 determined from analysis of the emissivity at ..delta..R=0.5 kpc intervals over the range 3< or =R< or =9 kpc. We thus verify the presence of a high density ring of giant molecular clouds midway between the Sun and the galactic center. The density of molecular hydrogen in this structure exceeds by a factor of 10 that of atomic hydrogen in the same region. Typical column densities of gas (H/sub 2/) observed looking through this ring at lapprox.30/sup 0/ are 4 x 10/sup 22/ cm/sup -2/ or A/sub v/approx.40 mag. These results validate the use of /sup 12/CO line observations for galactic mapping ofmore » the distribution of molecular gas, since the /sup 13/CO and /sup 12/CO emissivities show similar variations on a galactic scale. The similarity of the distribution from the two lines, which are quite disparate in optical depth, suggests that the /sup 12/CO line-integrated intensity in the galactic plane is a measure primarily of the number of clouds, and the temperature in the majority of the galactic plane H/sub 2/ is fairly similar (T/sub k/approx.10 K). The /sup 12/CO//sup 13/CO emissivity ratio changes by less than 40% between R=4 and R=8 kpc, although it is consistent with a constant isotopic abundance ratio within the error limits.« less