标题： TNG50模拟中类似银河系的星系周围的星系际介质——II：冷密气体云和高能云类比 显示英文标题

标题： The Circumgalactic Medium of Milky Way-like Galaxies in the TNG50 Simulation -- II: Cold, Dense Gas Clouds and High-Velocity Cloud Analogs

摘要： 我们利用IllustrisTNG项目的TNG50模拟来研究类似银河系星系周围星际介质（CGM）中的冷密气体云。 我们发现它们的CGM通常充满了大约数百（千）个适度（边缘）解析的云，这些云可能是高视向速度云（HVCs）的可能对应物。 从一个星系到另一个星系，云的丰度存在很大差异，我们所探索的云的物理属性——质量、大小、金属丰度、压力和动力学特性——也各不相同。 我们量化了云属性及其背景对比度的分布，为理想化模拟提供了宇宙学输入。 云的特征是亚太阳金属丰度、多样化的形状、小的过密度（$\chi = n_{\rm cold} / n_{\rm hot} \lesssim 10$）、主要是流入，并且旋转速度低于逃逸速度。 在TNG50分辨率下，解析的云的中位质量为$\sim 10^6\,\rm{M_\odot}$，大小为$\sim 10$千秒差距。 较大的云在数值上很好地收敛，而最小云的丰度随着分辨率增加而增加，正如预期的那样。 在TNG50类似的MW型晕中，相对于总压（热压），云相对于其周围的环境稍微（严重）欠压，这表明磁场可能很重要。 云在整个CGM中并非均匀分布，而是倾向于聚集在其他云附近，通常靠近富重子的卫星星系。 这表明至少有一些云来源于卫星，通过直接的冲激剥离或其他方式形成。 最后，我们将模拟结果与真实银河系晕中的中等和高速云观测结果进行了比较。 TNG50显示的云速度分布与观测结果相似，并预测了一组大量目前难以探测到的低速云。 显示英文摘要

摘要： We use the TNG50 simulation of the IllustrisTNG project to study cold, dense clouds of gas in the circumgalactic media (CGM) of Milky Way-like galaxies. We find that their CGM is typically filled with of order one hundred (thousand) reasonably (marginally) resolved clouds, possible analogs of high-velocity clouds (HVCs). There is a large variation in cloud abundance from galaxy to galaxy, and the physical properties of clouds that we explore -- mass, size, metallicity, pressure, and kinematics -- are also diverse. We quantify the distributions of cloud properties and cloud-background contrasts, providing cosmological inputs for idealized simulations. Clouds characteristically have sub-solar metallicities, diverse shapes, small overdensities ($\chi = n_{\rm cold} / n_{\rm hot} \lesssim 10$), are mostly inflowing, and have sub-virial rotation. At TNG50 resolution, resolved clouds have median masses of $\sim 10^6\,\rm{M_\odot}$ and sizes of $\sim 10$ kpc. Larger clouds are well converged numerically, while the abundance of the smallest clouds increases with resolution, as expected. In TNG50 MW-like haloes, clouds are slightly (severely) under-pressurised relative to their surroundings with respect to total (thermal) pressure, implying that magnetic fields may be important. Clouds are not distributed uniformly throughout the CGM, but are clustered around other clouds, often near baryon-rich satellite galaxies. This suggests that at least some clouds originate from satellites, via direct ram-pressure stripping or otherwise. Finally, we compare with observations of intermediate and high velocity clouds from the real Milky Way halo. TNG50 shows a similar cloud velocity distribution as observations, and predicts a significant population of currently difficult-to-detect low velocity clouds.