Ultra-luminous infrared galaxies are among the most luminous objects in the local universe and are thought to be powered by intense star formation. It has been shown that in these objects the rotational spectral lines of molecular hydrogen observed at mid-infrared wavelengths are not affected by dust obscuration, leaving unresolved the source of excitation of this emission. Here I report an analysis of archival Spitzer Space Telescope data on ultra-luminous infrared galaxies and demonstrate that star formation regions are buried inside optically thick clouds of gas and dust, so that dust obscuration affects star-formation indicators but not molecular hydrogen. I thereby establish that the emission of H_2 is not co-spatial with the buried starburst activity and originates outside the obscured regions. This is rather surprising in light of the standard view that H_2 emission is directly associated with star-formation activity. Instead, I propose that H_2 emission in these objects traces shocks in the surrounding material, which are in turn excited by interactions with nearby galaxies, and that powerful large-scale shocks cooling by means of H_2 emission may be much more common than previously thought. In the early universe, a boost in H_2 emission by this process may speed up the cooling of matter as it collapsed to form the first stars and galaxies and would make these first structures more readily observable.
Probing the Interstellar Medium of z~1 Ultra-luminous Infrared Galaxies through Interferometric Observations of CO and Spitzer Mid-infrared Spectroscopy
Quasar Radiative Feedback May Suppress Galaxy Growth on Intergalactic Scales at $z = 6.3$
Steward Observatory, University of Arizona（亚利桑那大学斯图尔德天文台）；School of Earth and Space Exploration, Arizona State University（亚利桑那州立大学地球与空间探索学院）；Augustana Campus, University of Alberta（阿尔伯塔大学奥古斯都校区）；MIT Kavli Institute for Astrophysics and Space Research（麻省理工学院卡弗里天体物理学与空间研究研究所）；Department of Physics, Massachusetts Institute of Technology（麻省理工学院物理系）；Center for Frontier Science, Chiba University（千叶大学前沿科学中心）；Department of Physics, University of Oxford（牛津大学物理系）；Department of Astronomy, Tsinghua University（清华大学天文系）；Division of Particle and Astrophysical Science, Nagoya University（名古屋大学粒子与天体物理科学分部）；Kavli Institute for Cosmology, University of Cambridge（剑桥大学卡弗里宇宙学研究所）；Cavendish Laboratory - Astrophysics Group, University of Cambridge（剑桥大学卡文迪许实验室天体物理组）；Department of Physics and Astronomy, University College London（伦敦大学学院物理与天文系）；AURA for the European Space Agency (ESA), Space Telescope Science Institute（欧洲航天局（ESA）授权机构AURA，太空望远镜科学研究所）；Department of Astronomy, University of Michigan（密歇根大学天文系）
A Massive Gas Outflow Outside the Line-of-Sight: Imaging Polarimetry of the Blue Excess Hot Dust Obscured Galaxy W0204-0506
Universidad Diego Portales（迭戈·波塔莱斯大学）；Astronomical Observatory（贝尔格莱德天文台）；Universiteit Gent（根特大学）；Caltech/IPAC（加州理工学院/IPAC）；Millennium Institute of Astrophysics（天体物理千年研究所）；Space Science Institute（空间科学研究所）；University of Leicester（莱斯特大学）；California Institute of Technology（加州理工学院）；Foundation for Research and Technology-Hellas (FORTH)（希腊研究与技术基金会）；European University Cyprus（塞浦路斯欧洲大学）；Jet Propulsion Laboratory（喷气推进实验室）；University of Crete（克里特大学）；Northwestern College（西北学院）；Chinese Academy of Sciences（中国科学院）；University of Chinese Academy of Sciences（中国科学院大学）；Beijing Normal University（北京师范大学）；University of Hertfordshire（赫特福德大学）；North-West University（西北大学）
