COLLISIONAL EXCITATION OF FAR-INFRARED LINE EMISSIONS FROM WARM INTERSTELLAR CARBON MONOXIDE (CO)
COLLISIONAL EXCITATION OF FAR-INFRARED LINE EMISSIONS FROM WARM INTERSTELLAR CARBON MONOXIDE (CO)
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温暖星际一氧化碳 (CO) 的远红外线发射的碰撞激发
DOI：
10.1088/0004-637x/749/2/125
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发表时间：
2012
期刊：
影响因子：
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通讯作者：
D. Neufeld
中科院分区：
文献类型：
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作者：
D. Neufeld
最近的观察与赫歇尔/PACS的动机，和新的速率系数的碰撞激发CO的可用性，激发温暖的天体物理CO的重新使用数值和分析方法。对于等温介质的情况，已经在气体温度（100-5000 K）和H2密度（103-109 cm−3）的宽范围内获得了结果，并以旋转图的形式呈现，其中每个磁子状态的柱密度的对数log（NJ/gJ）被绘制为每个状态的能量EJ的函数。对于Herschel/PACS可达到的波长范围内的旋转跃迁，当n（H2）<$108 cm−3时，这样的图几乎是线性的。当n（H2）<$106.8 -108 cm−3时，它们表现出显著的负曲率，而当n（H2）<$104.8 cm−3时，曲率在整个PACS可达范围内一致为正。因此，一个积极弯曲的CO转动图的观察并不一定需要存在多个温度分量。事实上，对于Herschel/PACS观察到的一些源，CO旋转图显示出适度的正曲率，可以用单个等温分量来解释。通常，所需的物理参数是104-105 cm−3范围内的密度和接近CO可以存活的最大温度。其他来源展示更多的曲率旋转图比可以占一个单一的温度分量。对于气体温度呈幂律分布的介质dN/dT B T−，H2密度为103-109 cm−3，幂律指数B在1-5范围内，得到了这样的结果;这样的介质可以解释CO转动图，它比等温介质产生的任何转动图都更正弯曲。
Motivated by recent observations with Herschel/PACS, and the availability of new rate coefficients for the collisional excitation of CO, the excitation of warm astrophysical CO is revisited with the use of numerical and analytic methods. For the case of an isothermal medium, results have been obtained for a wide range of gas temperatures (100–5000 K) and H2 densities (103–109 cm−3), and presented in the form of rotational diagrams, in which the logarithm of the column density per magnetic substate, log (NJ/gJ), is plotted for each state, as a function of its energy, EJ. For rotational transitions in the wavelength range accessible to Herschel/PACS, such diagrams are nearly linear when n(H2) ⩾ 108 cm−3. When n(H2) ∼ 106.8–108 cm−3, they exhibit significant negative curvature, whereas when n(H2) ⩽ 104.8 cm−3, the curvature is uniformly positive throughout the PACS-accessible range. Thus, the observation of a positively curved CO rotational diagram does not necessarily require the presence of multiple temperature components. Indeed, for some sources observed with Herschel/PACS, the CO rotational diagrams show a modest positive curvature that can be explained by a single isothermal component. Typically, the required physical parameters are densities in the 104–105 cm−3 range and temperatures close to the maximum at which CO can survive. Other sources exhibit rotational diagrams with more curvature than can be accounted for by a single temperature component. For the case of a medium with a power-law distribution of gas temperatures, dN/dT∝T−b, results have been obtained for H2 densities 103–109 cm−3 and power-law indices, b, in the range 1–5; such a medium can account for a CO rotational diagram that is more positively curved than any resulting from an isothermal medium.