We use spectral stacking to measure the contribution of galaxies of different masses and in different hierarchies to the cosmic atomic hydrogen (HI) mass density in the local Universe. Our sample includes 1793 galaxies at $z < 0.11$ observed with the Westerbork Synthesis Radio Telescope, for which Sloan Digital Sky Survey spectroscopy and hierarchy information are also available. We find a cosmic HI mass density of $Ω_{\rm HI} = (3.99 \pm 0.54)\times 10^{-4} h_{70}^{-1}$ at $\langle z\rangle = 0.065$. For the central and satellite galaxies, we obtain $Ω_{\rm HI}$ of $(3.51 \pm 0.49)\times 10^{-4} h_{70}^{-1}$ and $(0.90 \pm 0.16)\times 10^{-4} h_{70}^{-1}$, respectively. We show that galaxies above and below stellar masses of $\sim$10$^{9.3}$ M$_{\odot}$ contribute in roughly equal measure to the global value of $Ω_{\rm HI}$. While consistent with estimates based on targeted HI surveys, our results are in tension with previous theoretical work. We show that these differences are, at least partly, due to the empirical recipe used to set the partition between atomic and molecular hydrogen in semi-analytical models. Moreover, comparing our measurements with the cosmological semi-analytic models of galaxy formation {\sc Shark} and GALFORM reveals gradual stripping of gas via ram pressure works better to fully reproduce the properties of satellite galaxies in our sample, than strangulation. Our findings highlight the power of this approach in constraining theoretical models, and confirm the non-negligible contribution of massive galaxies to the HI mass budget of the local Universe.
Stacking 21-cm Maps around Lyman-$α$ Emitters during Reionization: Prospects for a Cross-correlation Detection with the Hydrogen Epoch of Reionization Array
Atomic hydrogen reservoirs in quiescent galaxies at z = 0.4
Università degli Studi di Padova（帕多瓦大学）；INAF - Osservatorio Astronomico di Padova（意大利国家天体物理研究所帕多瓦天文台）；National Center for Nuclear Research（波兰核研究中心）；SISSA（的里雅斯特高等研究学院）；Université de Genève（日内瓦大学）；Universität Zürich（苏黎世大学）；University of the Western Cape（西开普大学）；University of Cape Town（开普敦大学）；INAF - Istituto di Radioastronomia（意大利国家天体物理研究所射电天文台）
HI Depletion Begins Well Beyond the Virial Radius: A FAST Stacking Study of 36 Galaxy Clusters to 5R200
Chinese Academy of Sciences South America Center for Astronomy, National Astronomical Observatories, CAS（中国科学院南美天文中心，国家天文台）；Key Laboratory of Optical Astronomy, NAOC（国家天文台光学天文重点实验室）；National Astronomical Observatories, Chinese Academy of Sciences（中国科学院国家天文台）；Guizhou Radio Astronomical Observatory, Guizhou University（贵州大学贵州天文观测台）；Instituto de Física y Astronomía, Universidad de Valparaíso（瓦尔帕莱索大学物理与天文学研究所）；Millennium Nucleus for Galaxies (MINGAL)（星系千年核（MINGAL））；Universidad Tecnica Federico Santa Maria（费德里科·圣塔玛利亚理工大学）；School of Physics and Astronomy, Beijing Normal University（北京师范大学物理与天文学院）；Korea Astronomy and Space Science Institute（韩国天文与空间科学研究院）
Gas flows in the circumgalactic medium around simulated high-redshift galaxies
利用一个新的宇宙学变焦模拟样本，我们分析了红移范围z >= 3的模拟星系周围的环星系气体的性质。这些模拟旨在代表最近用MUSE仪器获得的莱曼α发射体的观测样本（晕质量约为10^10-10^11太阳质量）。我们发现，超新星反馈有显着的影响，流入和流出的环星系介质驱动外流，减少扩散流入率，并通过增加流入气体的中性部分。通过时间上叠加模拟输出，我们发现流入和流出阶段之间发生了显着的净质量交换：没有一个阶段是质量守恒的。特别是，我们发现，在中性流出的氢的质量随半径呈指数下降的气体从晕中心向外流动。这可能是由喷泉式循环过程和流出气体的逐渐光/碰撞电离的组合引起的。我们的模拟没有预测CGM中存在快速移动的中性流出。中性外流则以中等径向速度（约50 km ^-1）运动，大部分动能与切向运动而非径向运动有关。
