Cloud properties across spatial scales in simulations of the interstellar medium
Tine Colman, Noé Brucy, Philipp Girichidis, Simon C. O Glover, Milena Benedettini, Juan D. Soler, Robin G. Tress, Alessio Traficante, Patrick Hennebelle, Ralf S… 展开作者
Tine Colman, Noé Brucy, Philipp Girichidis, Simon C. O Glover, Milena Benedettini, Juan D. Soler, Robin G. Tress, Alessio Traficante, Patrick Hennebelle, Ralf S. Klessen, Sergio Molinari, Marc-Antoine Miville-Deschênes
备注：
22 pages, 16 figures, proposed for acceptance in A&A
本文利用 Hop 算法从多种星际介质模拟中提取分子云，发现尽管尺度与分辨率差异很大，云的质量谱、速度弥散和维里参数仍呈现稳健的标度关系，并与观测和理论基本一致。
摘要：
分子云（MC）是星际介质（ISM）中的致密气体结构，其尺度从十秒差距延伸至数百秒差距，构成了恒星形成可用的主要气体储库。不同复杂程度的流体动力学模拟是研究分子云演化及其性质的一种有前景的途径。然而，每个模拟通常在分辨率范围上有限，并且使用不同的云提取算法，这使得模拟之间的比较变得复杂。在本工作中，我们旨在从覆盖广泛空间尺度的不同模拟中提取云，并比较它们的性质，例如大小、形状、质量、内部速度弥散和维里状态。我们将 Hop 云检测算法应用于分层 ISM 盒子的（磁）流体动力学数值模拟以及使用 Flash、Ramses 和 Arepo 生成的孤立星系盘模拟。我们发现，在所有设置中，提取出的云在形状上都很复杂，从圆形天体到复杂的丝状网络不等。尽管尺度、分辨率和亚网格物理存在广泛差异，我们在所研究的度量指标中观察到了令人惊讶的稳健趋势。在模拟之间的重叠区域，质量谱无需重新标定即可匹配，并且具有与理论预测一致的高质量端斜率 $\mathrm{d} N/\mathrm{d}\ln M\propto-1$。对于大云（$R\gtrsim3\\,\mathrm{pc}$），内部速度弥散随云的大小按 $σ\propto R^{0.75}$ 标度。对于小云，我们发现与幂律标度相比 σ 更大，这与观测中所见一致，其原因是超新星驱动的湍流。几乎所有云在引力上都是非束缚的，维里参数按 $α_\mathrm{vir}\propto M^{-0.4}$ 标度，这比观测到的标度略平，但考虑到较大的弥散，仍与观测一致。
英文摘要：
Molecular clouds (MC) are structures of dense gas in the interstellar medium (ISM), that extend from ten to a few hundred parsecs and form the main gas reservoir available for star formation. Hydrodynamical simulations of varying complexity are a promising way to investigate MC evolution and their properties. However, each simulation typically has a limited range in resolution and different cloud extraction algorithms are used, which complicates the comparison between simulations. In this work, we aim to extract clouds from different simulations covering a wide range of spatial scales. We compare their properties, such as size, shape, mass, internal velocity dispersion and virial state. We apply the Hop cloud detection algorithm on (M)HD numerical simulations of stratified ISM boxes and isolated galactic disk simulations that were produced using Flash Ramses and Arepo We find that the extracted clouds are complex in shape ranging from round objects to complex filamentary networks in all setups. Despite the wide range of scales, resolution, and sub-grid physics, we observe surprisingly robust trends in the investigated metrics. The mass spectrum matches in the overlap between simulations without rescaling and with a high-mass slope of $\mathrm{d} N/\mathrm{d}\ln M\propto-1$ in accordance with theoretical predictions. The internal velocity dispersion scales with the size of the cloud as $σ\propto R^{0.75}$ for large clouds ($R\gtrsim3\,\mathrm{pc}$). For small clouds we find larger sigma compared to the power-law scaling, as seen in observations, which is due to supernova-driven turbulence. Almost all clouds are gravitationally unbound with the virial parameter scaling as $α_\mathrm{vir}\propto M^{-0.4}$, which is slightly flatter compared to observed scaling, but in agreement given the large scatter.
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Clustering and dynamics of nano-sized particles (nano dust) is investigated using high-resolution ($1024^3$) simulations of compressible isothermal hydrodynamic turbulence, intended to mimic the conditions inside cold molecular clouds in the interstellar medium. Nano-sized grains may cluster in a turbulent flow (small-scale clustering), which increases the local grain density significantly. Together with the increased interaction rate due to turbulent motions, aggregation of interstellar nano-dust may be plausible.
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The C(3P) + NH3 reaction in interstellar chemistry: II. Low temperature rate constants and modeling of NH, NH2 and NH3 abundances in dense interstellar clouds
Analysis of interstellar absorption lines observed in high-resolution {\em HST} spectra of nearby stars provides temperatures, turbulent velocities, and kinetic properties of warm interstellar clouds. Previous studies identified 15 warm partially ionized clouds within about 10~pc of the Sun and measured their mean thermal and kinematic properties. A new analysis of 100 interstellar velocity components reveals a wide range of temperatures and turbulent velocities within the Local Interstellar Cloud (LIC) and other nearby clouds. These variations appear to be random with Gaussian distributions. …
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In this paper we discuss and confront recent results on metallicity variations in the local interstellar medium, obtained from observations of HII regions and neutral clouds of the Galactic thin disk, and compare them with recent high-quality metallicity determinations of other tracers of the chemical composition of the interstellar medium as B-type stars, classical Cepheids and young clusters. We find that the metallicity variations obtained for these last kinds of objects are consistent with each other and with that obtained for HII regions but significantly smaller than those obtained for n…
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Context. Insight into the conditions that drive the physics and chemistry in interstellar clouds is gained from determining the abundance and charge state of their components. Aims. We propose an evaluation of the C60:C60+ ratio in diffuse and translucent interstellar clouds that exploits electronic absorption bands so as not to rely on ambiguous IR emission measurements. Methods. The ratio is determined by analyzing archival spectra and literature data. Information on the cation population is obtained from published characteristics of the main diffuse interstellar bands attributed to C60+ and…
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