We consider a model of the circumgalactic medium (CGM) in which feedback maintains a constant ratio of cooling time to freefall time throughout the halo, so that the entire CGM is marginally unstable to multiphase condensation. This 'precipitation model' is motivated by observations of multiphase gas in the cores of galaxy clusters and the halos of massive ellipticals. We derive from the model density and temperature profiles for the CGM around galaxies with masses similar to the Milky Way. After taking into consideration the geometrical position of our solar system in the Milky Way, we show that the CGM model is consistent with observed OVI, OVII, and OVIII column densities only if temperature fluctuations with a log-normal dispersion $σ_{\ln T} \sim 0.6$-$1.0$ are included. We show that OVI column densities observed around star-forming galaxies require systematically greater values of $σ_{\ln T}$ than around passive galaxies, implying a connection between star formation in the disk and the state of the CGM. Photoionization by an extra-galactic UV background does not significantly change these CGM features for galaxies like the Milky Way but has much greater and significant effects on the CGM of lower-mass galaxies.
The COS-Halos Survey: Origins of the Highly Ionized Circumgalactic Medium of Star-Forming Galaxies
扩散晕气体对星系重子预算的总贡献很大程度上取决于它的主要电离态。在本文中，我们解决的物理条件，在高度电离环星系介质（CGM）跟踪的OVI吸收线观测到的COS-Halos光谱。我们分析了所观察到的离子柱密度，吸收线宽度和相对速度，以及NV/OVI的比率为39拟合Voigt配置文件组件的OVI。我们比较这些数量与广泛的电离模型给出的预测。光电离模型，只包括河外紫外背景辐射被排除;保守地说，NV/OVI的上限和N $_{\rm OVI}$的测量意味着非物理的大路径长度> 100 kpc。此外，非常广泛的OVI吸收（b > 40 km s $^{-1}$）是一个定义的特征CGM的恒星形成的L* 星系。我们强调了两个可能的起源为大部分观察到的OVI：（1）高度结构化的气体云主要由当地的高能量源或（2）气体辐射冷却大尺度背后的超音速风。大约20%的环银河OVI不与$\pm$ 50 km s $^{-1}$内的任何低电离态气体对齐，并且仅在M $_{\rm halo}$ < 10 $^{12}$ M $_{\odot}$的晕中发现。我们认为，这种类型的不匹配的OVI吸收跟踪热电晕本身的特征温度为10 $^{5.5}$ K。我们讨论了这些非常不同的物理起源的动力学状态，气体冷却速率，和总重子含量的L* 气体晕的影响。
Kinematics of H I and O VI Absorbers: Insights into the Turbulence Driver of the Multiphase Circumgalactic Medium
Tsinghua University（清华大学）；The University of Chicago（芝加哥大学）；Peking University（北京大学）；Zentrum für Astronomie der Universität Heidelberg, Astronomisches Rechen-Institut（海德堡大学天文中心，天文计算研究所）
MUSEQuBES: Physical conditions, origins, and multi-element abundances of the circumgalactic medium of an isolated, star-forming dwarf galaxy at z=0.57
University of Michigan（密歇根大学）；Inter-University Centre for Astronomy & Astrophysics（天文学与天体物理学跨大学中心）；The Observatories of the Carnegie Institution for Science（卡内基科学机构天文台）；University of North Texas（北德克萨斯大学）；Tsinghua University（清华大学）；The University of Chicago（芝加哥大学）；Northwestern University（西北大学）；Tel Aviv University（特拉维夫大学）
