Simulating the atomic and molecular content of molecular clouds using probability distributions of physical parameters
Simulating the atomic and molecular content of molecular clouds using probability distributions of physical parameters
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DOI：
10.1093/mnras/stz405
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发表时间：
2019-05-01
影响因子：
4.8
通讯作者：
van Dishoeck, Ewine F.
中科院分区：
文献类型：
--
作者：
Bisbas, Thomas G.;Schruba, Andreas;van Dishoeck, Ewine F.
对星系中的星际介质（ISM）的现代观测发现了各种原子和分子物种。我们的目标是将这些观测结果与ISM的天体化学性质联系起来。3D水化学模拟尝试了这一点，但由于极端的计算成本，它们必须依赖于简化的化学网络，并绑定到个别案例研究。我们提出了一种替代方法，该方法通过预先计算的1D热化学光解离区域（PDR）计算确定原子和分子物种的丰度和激发，在更大的尺度上模拟ISM。我们采用对数正态分布的列密度（AV-PDF），每个列密度与流体动力学模拟得出的体积密度。我们考虑两个对数正态AV-PDF：一个弥漫的，低密度的介质，平均可见消光（A（V））在酒吧= 0.75等和色散的s = 0.5和一个更密集的巨大的分子云（A（V））在酒吧= 4等和西格玛= 0.8。我们把紫外辐射场，宇宙射线电离率，和金属丰度作为自由参数。我们发现，低密度介质仍然完全HI和C II占主导地位的所有探索条件下。密度较大的云几乎总是保持分子（即。e. H-2主导的），而其碳相（CO，C I，和CII）是敏感的上述自由参数，这意味着现有的方法跟踪富H-2气体可能需要调整，取决于环境。我们的数值框架可用于估计大型ISM区域的PDR属性，并量化具有不同环境参数的趋势，因为它速度快，覆盖广泛的参数空间，并且扩展灵活。
Modern observations of the interstellarmedium (ISM) in galaxies detect a variety of atomic and molecular species. The goal is to connect these observations to the astrochemical properties of the ISM. 3D hydro-chemical simulations attempt this but due to extreme computational cost, they have to rely on simplified chemical networks and are bound to individual case studies. We present an alternative approach which models the ISM at larger scales by an ensemble of pre-calculated 1D thermo-chemical photodissociation region (PDR) calculations that determine the abundance and excitation of atomic and molecular species. We adopt lognormal distributions of column density (AV-PDFs) for which each column density is linked to a volume density as derived by hydrodynamical simulations. We consider two lognormal AV-PDFs: a diffuse, low-density medium with average visual extinction of (A(V)) over bar = 0.75 mag and dispersion of s = 0.5 and a denser giant molecular cloud with (A(V)) over bar = 4mag and sigma = 0.8. We treat the UV radiation field, cosmic ray ionization rate, and metallicity as free parameters. We find that the low-density medium remains fully HI- and C II-dominated under all explored conditions. The denser cloud remains almost always molecular (i. e. H-2-dominated) while its carbon phase (CO, C I, and CII) is sensitive to the above free parameters, implying that existing methods of tracing H-2-rich gas may require adjustments depending on environment. Our numerical framework can be used to estimate the PDR properties of large ISM regions and quantify trends with different environmental parameters as it is fast, covers wide parameter space, and is flexible for extensions.