The Impact of Enhanced Halo Resolution on the Simulated Circumgalactic Medium
The Impact of Enhanced Halo Resolution on the Simulated Circumgalactic Medium
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DOI：
10.3847/1538-4357/ab378f
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发表时间：
2018-11
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通讯作者：
C. Hummels;Britton D. Smith;P. Hopkins;B. O’Shea;Devin W. Silvia;J. Werk;N. Lehner;J. Wise;D. Collins;Iryna S. Butsky
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作者：
C. Hummels;Britton D. Smith;P. Hopkins;B. O’Shea;Devin W. Silvia;J. Werk;N. Lehner;J. Wise;D. Collins;Iryna S. Butsky
传统的宇宙流体动力学模拟无法在空间上分辨环绕星系的介质（CGM），即围绕星系并延伸到其维里半径的稀薄气体的储存库。我们介绍了增强晕分辨率（EHR）的技术，使更逼真的物理建模的模拟CGM不断迫使气体细化到更小的尺度在整个模拟星系的维里晕。我们调查的EHR在风暴模拟，一套enzo为基础的宇宙学变焦模拟L* 星系的演变，解决空间尺度500 comoving pc出100 comoving kpc的银河系中心半径的影响。在其众多效应中，EHR（1）改变CGM的热平衡，增加其冷气体含量并减少其暖/热气体含量;（2）在较长时间内保持冷气体结构;（3）使这些冷云以逐渐变小的尺寸尺度存在。在观察上，这导致在整个CGM中“低离子”（如H1）的增加和“高离子”（如Ovi）的下降。EHR的这些效应在风暴模拟中并不收敛，但推断这些趋势表明，CGM实际上是一种雾，由悬浮在介质中的晕维里温度下的无处不在的、小的、长寿命的冷云组成。我们发现EHR通过以下方式产生上述效果：（1）更好地采样CGM相的分布，使相分布的致密冷尾部能够失控冷却;以及（2）防止冷气体云与环境热晕人工混合并蒸发。
Traditional cosmological hydrodynamics simulations fail to spatially resolve the circumgalactic medium (CGM), the reservoir of tenuous gas surrounding a galaxy and extending to its virial radius. We introduce the technique of Enhanced Halo Resolution (EHR), enabling more realistic physical modeling of the simulated CGM by consistently forcing gas refinement to smaller scales throughout the virial halo of a simulated galaxy. We investigate the effects of EHR in the tempest simulations, a suite of enzo-based cosmological zoom simulations following the evolution of an L* galaxy, resolving spatial scales of 500 comoving pc out to 100 comoving kpc in galactocentric radius. Among its many effects, EHR (1) changes the thermal balance of the CGM, increasing its cool gas content and decreasing its warm/hot gas content; (2) preserves cool gas structures for longer periods; and (3) enables these cool clouds to exist at progressively smaller size scales. Observationally, this results in a boost in “low ions” like H i and a drop in “high ions” like O vi throughout the CGM. These effects of EHR do not converge in the tempest simulations, but extrapolating these trends suggests that the CGM is actually a mist consisting of ubiquitous, small, long-lived, cool clouds suspended in a medium at the halo virial temperature. We find that EHR produces the above effects by (1) better sampling the distribution of CGM phases, enabling runaway cooling in the dense, cool tail of the phase distribution; and (2) preventing cool gas clouds from artificially mixing with the ambient hot halo and evaporating.