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arXiv 2406.06702astro-ph.GA
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NEATH III:模拟恒星形成云分子谱线巡天

NEATH III: a molecular line survey of a simulated star-forming cloud

F. D. Priestley, P. C. Clark, S. C. O. Glover, S. E. Ragan, O. Fehér, L. R. Prole, R. S. Klessen

AI总结:

本文通过自洽动力学与化学演化模拟,系统研究了分子云中CO同位素及多种致密气体示踪剂的谱线发射,发现N₂H⁺是优于HCN的高密度气体示踪剂,并证明大尺度环境对前恒星核谱线性质有重要影响,孤立核模型不足以解释观测。

摘要:

我们展示了对一个模拟分子云的合成谱线观测,采用了动力学与时间相关化学演化的自洽处理方法。我们研究了三种最常见的CO同位素分子($^{12}$CO、$^{13}$CO、C$^{18}$O)和六种被认为示踪致密气体的分子(NH$_3$、HCN、N$_2$H$^+$、HCO$^+$、CS、HNC)的谱线发射。我们的模拟产生了一系列与实际分子云中观测结果一致的谱线强度。HCN与CO的强度比随柱密度变化相对不敏感,这使得HCN(以及化学性质相似的物种如CS)成为云中高密度物质的较差示踪剂。另一方面,N$_2$H$^+$与HCN或CO的比值对柱密度高于$10^{22} \, {\ m cm^{-2}}$的区域具有高度选择性,并且N$_2$H$^+$谱线是高体积密度($>10^4 \, {\ m cm^{-3}}$)物质动力学的非常好的示踪剂。聚焦于模拟云中形成的核,我们发现其谱线强度与一个前恒星核观测样本的谱线强度吻合良好,包括在硫元素丰度未耗尽的条件下再现了观测到的CS谱线强度。然而,模拟中形成的核与具有其他方面可比性质的孤立核模型之间的一致性较差。来自大尺度环境的形成过程及其与环境的相互作用对核的谱线发射性质有显著影响,使得孤立模型不适合用于解释观测数据。

英文摘要:

We present synthetic line observations of a simulated molecular cloud, utilising a self-consistent treatment of the dynamics and time-dependent chemical evolution. We investigate line emission from the three most common CO isotopologues ($^{12}$CO, $^{13}$CO, C$^{18}$O) and six supposed tracers of dense gas (NH$_3$, HCN, N$_2$H$^+$, HCO$^+$, CS, HNC). Our simulation produces a range of line intensities consistent with that observed in real molecular clouds. The HCN-to-CO intensity ratio is relatively invariant with column density, making HCN (and chemically-similar species such as CS) a poor tracer of high-density material in the cloud. The ratio of N$_2$H$^+$ to HCN or CO, on the other hand, is highly selective of regions with densities above $10^{22} \, {\rm cm^{-2}}$, and the N$_2$H$^+$ line is a very good tracer of the dynamics of high volume density ($>10^4 \, {\rm cm^{-3}}$) material. Focusing on cores formed within the simulated cloud, we find good agreement with the line intensities of an observational sample of prestellar cores, including reproducing observed CS line intensities with an undepleted elemental abundance of sulphur. However, agreement between cores formed in the simulation, and models of isolated cores which have otherwise-comparable properties, is poor. The formation from and interaction with the large-scale environment has a significant impact on the line emission properties of the cores, making isolated models unsuitable for interpreting observational data.

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