Massive stars produce copious quantities of ultraviolet radiation beyond the Lyman limit, photoionizing the interstellar medium (ISM) and producing H II regions. As strong sources of recombination- and forbidden-line emission, infrared continuum, and thermal (free-free) radio continuum, H II regions serve as readily-observable beacons of massive star formation in the Milky Way and external galaxies. Along with supernovae, H II regions are dominant sources of feedback in star-forming galaxies, injecting radiative and mechanical luminosity into the ISM. H II regions may prove more important than supernovae as triggers of star formation through localized compression of cold cloud cores. In this review, I give a broad overview of the structure and time-evolution of H II regions, emphasizing complications to the theoretical picture revealed by multiwavelength observations. I discuss a recent controversy surrounding the dominant feedback mechanism in 30 Doradus, the most luminous H II region in the Local Group. I summarize the first results from the Milky Way Project (MWP), which has produced a new catalog of several thousand candidate Galactic H II regions by enlisting >35,000 "citizen scientists" to search Spitzer Space Telescope survey images for bubble-shaped structures. The MWP and similar large catalogs enable empirical studies of Galactic H II region evolution across the full range of luminosities and statistical studies of triggered star formation.
Bound or blown: the fate of hot gas in galaxy groups
University of Geneva（日内瓦大学）；Leiden University（莱顿大学）；Max-Planck-Institut für Astronomie（马克斯·普朗克天文学研究所）；Lorentz Institute for Theoretical Physics, Leiden University（莱顿大学洛伦兹理论物理研究所）；University of Colorado（科罗拉多大学）；Center for Astrophysics | Harvard & Smithsonian（哈佛与史密森尼天体物理中心）；INAF, Istituto di Astrofisica Spaziale e Fisica Cosmica di Milano（意大利国家天体物理研究所米兰空间天体物理与宇宙物理研究所）；University of Hertfordshire（赫特福德大学）；Kavli Institute for Cosmology, University of Cambridge（剑桥大学卡弗里宇宙学研究所）；University of Alabama in Huntsville（阿拉巴马大学亨茨维尔分校）；University of Helsinki（赫尔辛基大学）
通过XMM-Newton Group AGN项目样本与FLAMINGO模拟对比，研究AGN反馈对星系团热气体含量的影响，发现中等反馈模型与观测数据最吻合，而极端反馈模型被排除。
