标题： 超亮红外星系中的 H₂ 发射产生于光解离区之外 显示英文标题

标题： H_2 emission arises outside photodissociation regions in ultra-luminous infrared galaxies

摘要： 极亮红外星系是局部宇宙中最亮的天体之一，被认为是由剧烈的恒星形成所驱动。 已经表明，在这些星系中，于中红外波段观测到的分子氢的转动光谱线并未受到尘埃遮蔽的影响，但仍未解决激发这种发射的来源问题。 在此，我报告了对存档的斯皮策太空望远镜数据关于极亮红外星系的分析，并证明恒星形成区埋藏在光学厚度较大的气体和尘埃云中，因此尘埃遮蔽会影响恒星形成指示器，但不会影响分子氢。 由此确立了H_2 的发射与埋藏的恒星爆发活动并不共面，并且起源于被遮蔽的区域之外。 这与H_2 发射直接与恒星形成活动相关的标准观点大相径庭。 相反，我认为这些星系中的H_2 发射追踪了周围物质中的激波，而这些激波又由与附近星系的相互作用激发。并且，通过H_2 发射冷却的强大大规模激波可能比之前认为的更为普遍。 在早期宇宙中，通过这种方式增强的H_2 发射可能会加速物质在塌缩形成第一颗恒星和星系时的冷却过程，并使这些最初的结构更容易被观测到。 显示英文摘要

摘要： 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.