星系碰撞碎片中的可见和不可见分子气体
Visible and invisible molecular gas in collisional debris of galaxies
摘要：
在一些相互作用星系的碰撞碎片中，分子气体已经被搜索并发现了出乎意料的大量：富含HI的潮汐尾，桥和碰撞环。到目前为止，它是通过对CO线的毫米观测而被观测到的，并在与氢原子密集凝聚有关的恒星形成区域或附近被探测到。冷H2的发现距离母星系（碰撞）大于50 kpc，而螺旋星系的外盘通常被认为是CO贫乏的，这对它的起源提出了质疑，并支持了坍缩HI云的本地生产假设。然而，最近的观测扩散CO组分沿潮汐碎片挑战了这一想法。最近的另一个难题是测量两个相互作用的系统和四个质量缺失的回收物体的碰撞碎片，而那里预计没有暗物质。一种有争议的解释是，这种看不见的成分是最初存在于螺旋盘中的冷的、“看不见的”分子气体。
英文摘要：
Molecular gas has been searched for and found in unexpectedly large quantities in some collisional debris of interacting galaxies: HI-rich tidal tails, bridges and collisional rings. It was so far observed through millimeter observations of the CO line and detected towards or near regions of star-formation associated to dense condensations of the atomic hydrogen. The discovery of cool H2 at distances greater than 50 kpc from the parent (colliding) galaxies, whereas the external disk of spirals is generally considered to be CO-poor, raised question on its origin and favored the hypothesis of a local production out of collapsed HI clouds. However recent observations of a diffuse CO component along tidal debris have challenged this idea. Another recent puzzle is the measurement in the collisional debris of two interacting systems and four recycled objects of a missing mass, whereas no dark matter is expected there. One debated interpretation is that this unseen component is cold, "invisible" molecular gas initially present in the disk of spirals.
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