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首页> 外文期刊>The Astrophysical journal >A COMPARISON OF ~13CO LOCAL THERMODYNAMIC EQUILIBRIUM AND TRUE COLUMN DENSITIES IN MOLECULAR CLOUD MODELS PAOLO PANOAN
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A COMPARISON OF ~13CO LOCAL THERMODYNAMIC EQUILIBRIUM AND TRUE COLUMN DENSITIES IN MOLECULAR CLOUD MODELS PAOLO PANOAN

机译：分子云模型中〜13CO局部热力学平衡与真柱密度的比较

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摘要

In this work we use models of molecular clouds and non-LTE radiative transfer calculations to compare the column densities of molecular clouds with their LTE ~13CO column densities. The cloud models consist of three-dimensional grids of density and velocity fields obtained as solutions of the com- pressible magnetohydrodynamic equations in a 1283 periodic grid in both the supersonic and super- AlfVenic regimes. Because of the random nature of the velocity field and the presence of shocks, the densities span a continuous range of values covering about 6 orders of magnitude (from 0.1 to 10~5 cm~-3). As a result, the LTE column densities can be calculated over 3 orders of magnitude. We find that LTE column densities of molecular clouds typically underestimate the mean ~13CO true column densities by factors ranging from 1.3 to 7. These results imply that the standard LTE methods for the derivation of column densities from CO data systematically underestimate the true values independent of other major sources of uncertainty such as the relative abundance of CO.
机译：在这项工作中，我们使用分子云模型和非LTE辐射转移计算来比较分子云的列密度与其LTE〜13CO列密度。云模型由密度和速度场的三维网格组成，这些三维网格是在超音速和超AlfVenic体制下的1283个周期网格中的可压缩磁流体动力学方程的解。由于速度场的随机性质和震动的存在，密度跨越了连续的值范围，覆盖了大约6个数量级（从0.1到10〜5 cm〜-3）。结果，可以在3个数量级上计算LTE列密度。我们发现分子云的LTE色谱柱密度通常会低估平均〜13CO的实际色谱柱密度，范围为1.3到7。这些结果表明，用于从CO数据推导色谱柱密度的标准LTE方法系统地低估了与其他主要的不确定性来源，例如一氧化碳的相对丰度。

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