arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 1507.07565astro-ph.GA
收藏

NGC 6240分子气体的模拟

Modelling the Molecular Gas in NGC 6240

R. Tunnard, T. R. Greve, S. Garcia-Burillo, J. Graciá Carpio, A. Fuente, L. Tacconi, R. Neri, A. Usero

备注：
27 pages, 17 figures, 9 tables. Accepted in ApJ
阅读 PDF
arXiv 页面 ↗HTML 原文 ↗

摘要：

我们首次用IRAM PdBI观测到NGC 1，6240中的H $^{13}$ CN $(1-0)$、H $^{13}$ CO $^+(1-0)$和SiO $(2-1)$。结合马尔可夫链蒙特卡罗（MCMC）代码与大速度梯度（LVG）建模，并从文献中获得额外的数据，我们同时适合三个气相和六个分子种类来约束分子气体的物理条件，包括质量$-$光度转换因子。我们发现在冷的稠密云（$T_{\rm k}\sim10$ \，K，$n_{{\rm H}_2}\sim10^6$ \，cm $^{-3}$）中稠密分子气体的$\sim10^{10}M_\odot$，其体积填充因子为$<0.002$，嵌入在冲击加热的分子介质（$T_{\rm k}\sim2000$ \，K，$n_{{\rm H}_2}\sim10^{3.6}$ \，cm $^{-3}$）中，两者都被扩展的扩散相（$T_{\rm k}\sim200$ \，K，$n_{{\rm H}_2}\sim10^{2.5}$ \，cm $^{-3}$）包围。我们推导出一个全球性的$α_{\rm CO}=1.5^{7.1}_{1.1}$与气体质量$\log_{10}\left(M / [M_\odot]\right)=10.1_{10.0}^{10.8}$，占主导地位的致密气体。我们还发现了$α_{\rm HCN} = 32^{89}_{13}$，它追踪了冷的致密气体。[ $^{12}$ C]/[ $^{13}$ C]比值仅略微升高（$98^{230}_{65}$），与文献中报告的极高[CO]/[ $^{13}$ CO]比值（300-500）相反。然而，我们发现非常高的[HCN]/[H $^{13}$ CN]和[HCO $^+$ ]/[H $^{13}$ CO $^+$ ]丰度比$(300^{500}_{200})$，我们将其归因于冷稠密云中的同位素分馏。

英文摘要：

We present the first observations of H$^{13}$CN$(1-0)$, H$^{13}$CO$^+(1-0)$ and SiO$(2-1)$ in NGC\,6240, obtained with the IRAM PdBI. Combining a Markov Chain Monte Carlo (MCMC) code with Large Velocity Gradient (LVG) modelling, and with additional data from the literature, we simultaneously fit three gas phases and six molecular species to constrain the physical condition of the molecular gas, including mass$-$luminosity conversion factors. We find $\sim10^{10}M_\odot$ of dense molecular gas in cold, dense clouds ($T_{\rm k}\sim10$\,K, $n_{{\rm H}_2}\sim10^6$\,cm$^{-3}$) with a volume filling factor $<0.002$, embedded in a shock heated molecular medium ($T_{\rm k}\sim2000$\,K, $n_{{\rm H}_2}\sim10^{3.6}$\,cm$^{-3}$), both surrounded by an extended diffuse phase ($T_{\rm k}\sim200$\,K, $n_{{\rm H}_2}\sim10^{2.5}$\,cm$^{-3}$). We derive a global $α_{\rm CO}=1.5^{7.1}_{1.1}$ with gas masses $\log_{10}\left(M / [M_\odot]\right)=10.1_{10.0}^{10.8}$, dominated by the dense gas. We also find $α_{\rm HCN} = 32^{89}_{13}$, which traces the cold, dense gas. The [$^{12}$C]/[$^{13}$C] ratio is only slightly elevated ($98^{230}_{65}$), contrary to the very high [CO]/[$^{13}$CO] ratio (300-500) reported in the literature. However, we find very high [HCN]/[H$^{13}$CN] and [HCO$^+$]/[H$^{13}$CO$^+$] abundance ratios $(300^{500}_{200})$ which we attribute to isotope fractionation in the cold, dense clouds.

机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。

↑