论文标题
PDFCHEM：一种使用概率分布来确定ISM属性和推断环境参数的新快速方法
PDFchem: A new fast method to determine ISM properties and infer environmental parameters using probability distributions
论文作者
论文摘要
确定星际介质（ISM）的原子和分子含量作为环境参数的函数对于了解整个时期的恒星形成过程至关重要。尽管存在各种三维水力化学代码，以不同的尺度和红移对ISM进行建模，但它们在计算上很昂贵，并且在大型参数空间上的研究效率低下。在我们较早的方法的基础上，我们提出了PDFCHEM，这是一种新型算法，使用连接本地数量（$ a _ {\ rm v，eff} $）和观察到的量的功能，以中等和大的规模对冷ISM进行建模（$ a _ {\ rm v，eff} $）和观察到的（$ a _ _ _ {\ rm v，obs} $概率，以及局部数量dmentiment，$ n $ n y; $ a _ {\ rm v，obs} $的函数（pdf）在云尺度上通常是数十百个PC作为输入。对于任何给定的$ a _ {\ rm v，obs} $ - pdf，用数千个云进行采样，算法立即计算最重要物种的平均丰度（hi，h $ _2 $，cii，cii，ci，ci，ci，ci，co，oh oh oh oh $^+$，$^+$，h $ _2 $ o $ $ o $^+$ $ $ $^+$ $^+）在最常见的线（[CII]〜$158μ$ m，均为[CI]精细结构线和$^{12} $ CO的前五个旋转过渡）中。我们检查了两个$ a _ {\ rm V，obs} $ - PDFS在各种环境参数组合下对应于非星形成和星形成ISM区域。这些封面fuv强度在$χ/χ_0= 10^{ - 1} -10^3 $，宇宙射线电离速率的范围内，$ζ_ {\ rm cr} = 10^{ - 17} { - 17} -10} -10} -10^{ - 13}} { - 13}} $ z = 0.1-2 \，{\ rm z} _ {\ odot} $。 PDFCHEM快速，易于使用，再现了耗时的流体动力学模型的PDR量，可以直接与观察到的数据一起使用，以了解冷ISM化学的演变。
Determining the atomic and molecular content of the interstellar medium (ISM) as a function of environmental parameters is of fundamental importance to understand the star-formation process across the epochs. Although there exist various three-dimensional hydro-chemical codes modelling the ISM at different scales and redshifts, they are computationally expensive and inefficient for studies over a large parameter space. Building on our earlier approach, we present PDFchem, a novel algorithm that models the cold ISM at moderate and large scales using functions connecting the quantities of the local ($A_{\rm V,eff}$) and the observed ($A_{\rm V,obs}$) visual extinctions, and the local number density, $n_{\rm H}$, with probability density functions (PDF) of $A_{\rm V,obs}$ on cloud scales typically tens-to-hundreds of pc as an input. For any given $A_{\rm V,obs}$-PDF, sampled with thousands of clouds, the algorithm instantly computes the average abundances of the most important species (HI, H$_2$, CII, CI, CO, OH, OH$^+$, H$_2$O$^+$, CH, HCO$^+$) and performs radiative transfer calculations to estimate the average emission of the most commonly observed lines ([CII]~$158μ$m, both [CI] fine-structure lines and the first five rotational transitions of $^{12}$CO). We examine two $A_{\rm V,obs}$-PDFs corresponding to a non star-forming and a star-forming ISM region, under a variety of environmental parameters combinations. These cover FUV intensities in the range of $χ/χ_0=10^{-1}-10^3$, cosmic-ray ionization rates in the range of $ζ_{\rm CR}=10^{-17}-10^{-13}\,{\rm s}^{-1}$ and metallicities in the range of $Z=0.1-2\,{\rm Z}_{\odot}$. PDFchem is fast, easy to use, reproduces the PDR quantities of the time-consuming hydrodynamical models and can be used directly with observed data to understand the evolution of the cold ISM chemistry.
