论文标题
水冰沉积和分子云的生长
Water Ice Deposition and Growth in Molecular Clouds
论文作者
论文摘要
在星际云中，水冰沉积在谷物上仅发生在一定阈值a_th的视觉灭绝上。在灭绝大于a_th的情况下，水冰的推断柱密度与A_V之间存在（几乎是线性的）相关性。对于金牛座，蛇和罗载体等单个云配合物，A_TH和相关的梯度在所有视线范围内都非常相似。我们已经研究了这种现象的起源，并仔细考虑了可能涉及的各种可能机制，并应用了一个完整的化学模型来分析静态分子云中的行为和敏感性。我们的关键结果是：（i）现象的普遍性指向一个共同的原因，因此，视力探针区域具有相似，高级，化学和动力学进化的区域，（ii）对于金牛座和蛇源性而言； A_TH和相关的斜率可以是由于氧原子的冷冻和H2O分子的光do剂的平衡而产生的。没有其他机制可以令人满意地解释这种现象，（iii）a_th取决于局部密度，表明局部体积密度与柱密度与柱密度之间存在相关性，（iv）金牛座和蛇形的A_TH值的不同值可能是由于本地平均值强度，（v）的含量很小（V），<0的是，<0. <0. <0. <0. <0。除非有复杂的微观结构和/或修改对灭绝特征的修改，否则在Rho-ophiuchi中观察到的A_Th值很高。
In interstellar clouds the deposition of water ice onto grains only occurs at visual extinctions above some threshold value A_th. At extinctions greater than A_th there is a (near-linear) correlation between the inferred column density of the water ice and A_V. For individual cloud complexes such as Taurus, Serpens and Rho-Ophiuchi, A_th and the gradients of the correlation are very similar along all lines of sight. We have investigated the origin of this phenomenon, with careful consideration of the various possible mechanisms that may be involved and have applied a full chemical model to analyse the behaviours and sensitivities in quiescent molecular clouds. Our key results are: (i) the ubiquity of the phenomenon points to a common cause, so that the lines of sight probe regions with similar, advanced, chemical and dynamical evolution, (ii) for Taurus and Serpens; A_th and the slope of the correlation can be explained as resulting from the balance of freeze-out of oxygen atoms and photodesorption of H2O molecules. No other mechanism can satisfactorily explain the phenomenon, (iii) A_th depends on the local density, suggesting that there is a correlation between local volume density and column density, (iv) the different values of A_th for Taurus and Serpens are probably due to variations in the local mean radiation field strength, (v) most ice is accreted onto grains that are initially very small (<0.01 microns), and (vi) the very high value of A_th observed in Rho-Ophiuchi cannot be explained in the same way, unless there is complex microstructure and/or a modification to the extinction characteristics.
