Thermal instability in the CGM of L ⋆ galaxies: testing ‘precipitation’ models with the FIRE simulations
Thermal instability in the CGM of L ⋆ galaxies: testing ‘precipitation’ models with the FIRE simulations
复制标题
L 星系 CGM 中的热不稳定性：使用 FIRE 模拟测试“降水”模型
DOI：
10.1093/mnras/stab1281
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发表时间：
2021
影响因子：
4.8
通讯作者：
Wetzel, Andrew
中科院分区：
文献类型：
--
作者：
Esmerian, Clarke J;Kravtsov, Andrey V;Hafen, Zachary;Faucher-Giguère, Claude-André;Quataert, Eliot;Stern, Jonathan;Kereš, Dušan;Wetzel, Andrew
我们研究的热力学状态和冷却的低zcircumgalactic介质（CGM）在五个消防-2银河系质量的星系形成模拟。我们发现，在这些模拟中的CGM一般是多相的和动态的，与广泛的频谱主要是非线性的密度扰动源的气体从星系际介质（IGM）的吸积和流出的中央和卫星星系。我们调查的CGM的多相结构的起源与粒子跟踪分析，发现大部分的低熵气体已经从热晕冷却作为由这些扰动引发的热不稳定性的结果。CGM热分量的冷却与自由落体时间尺度stcool/tffin的比值在给定半径下跨越很宽的范围，为0.1 Rvir <r<Rvir，但在所有半径下，其中值近似为0.5 −20。这些与ICM“降水”模型中通常用作热不稳定阈值的≈10 - 20值相似。因此，一个一维模型的基础上的constanttcool/tffand流体静力学平衡的假设近似再现的数量密度和熵分布的每个模拟，但只有当它假设的金属丰度分布和温度边界条件直接从模拟。我们明确表明，thetcool/tffvalue的气体包裹在热组件的CGM不预测其随后吸积到中央星系的概率。这表明，tcool/tffis的值是一个差的预测的热稳定性的气体晕，其中大振幅的密度扰动是普遍的。
We examine the thermodynamic state and cooling of the low-zcircumgalactic medium (CGM) in five FIRE-2 galaxy formation simulations of Milky Way-mass galaxies. We find that the CGM in these simulations is generally multiphase and dynamic, with a wide spectrum of largely non-linear density perturbations sourced by the accretion of gas from the intergalactic medium (IGM) and outflows from both the central and satellite galaxies. We investigate the origin of the multiphase structure of the CGM with a particle-tracking analysis and find that most of the low-entropy gas has cooled from the hot halo as a result of thermal instability triggered by these perturbations. The ratio of cooling to free-fall time-scalestcool/tffin the hot component of the CGM spans a wide range of ∼1−100 at a given radius but exhibits approximately constant median values of ∼5−20 at all radii 0.1Rvir<r<Rvir. These are similar to the ≈10−20 value typically adopted as the thermal instability threshold in ‘precipitation’ models of the ICM. Consequently, a one-dimensional model based on the assumption of a constanttcool/tffand hydrostatic equilibrium approximately reproduces the number density and entropy profiles of each simulation but only if it assumes the metallicity profile and temperature boundary condition taken directly from the simulation. We explicitly show that thetcool/tffvalue of a gas parcel in the hot component of the CGM does not predict its probability of subsequently accreting on to the central galaxy. This suggests that the value oftcool/tffis a poor predictor of thermal stability in gaseous haloes in which large-amplitude density perturbations are prevalent.