Title: Galaxy disks do not need to survive in the L-CDM paradigm: the galaxy merger rate out to z~1.5 from morpho-kinematic data Show Chinese title

Title: 在L-CDM范式下，星系盘不需要幸存下来：基于形态-动力学数据的z~1.5范围内的星系并合率

Abstract: About two-thirds of present-day, large galaxies are spirals such as the Milky Way or Andromeda, but the way their thin rotating disks formed remains uncertain. Observations have revealed that half of their progenitors, six billion years ago, had peculiar morphologies and/or kinematics, which exclude them from the Hubble sequence. Major mergers, i.e., fusions between galaxies of similar mass, are found to be the likeliest driver for such strong peculiarities. However, thin disks are fragile and easily destroyed by such violent collisions, which creates a critical tension between the observed fraction of thin disks and their survival within the L-CDM paradigm. Here we show that the observed high occurrence of mergers amongst their progenitors is only apparent and is resolved when using morpho-kinematic observations which are sensitive to all the phases of the merging process. This provides an original way of narrowing down observational estimates of the galaxy merger rate and leads to a perfect match with predictions by state-of-the-art L-CDM semi-empirical models with no particular fine-tuning needed. These results imply that half of local thin disks do not survive but are actually rebuilt after a gas-rich major merger occurring in the past nine billion years, i.e., two-thirds of the lifetime of the Universe. This emphasizes the need to study how thin disks can form in halos with a more active merger history than previously considered, and to investigate what is the origin of the gas reservoir from which local disks would reform. Show Chinese abstract

Abstract: 如今大约三分之二的大星系是旋涡星系，比如银河系或者仙女座星系，但它们薄而旋转的盘状结构是如何形成的仍不确定。观测显示，六亿年前这些星系的一半祖先具有奇特的形态和/或动力学特性，这使它们排除在哈勃序列之外。重大合并（即质量相似的星系之间的融合）被认为是造成这种强烈奇特性的最可能原因。然而，薄盘是非常脆弱的，并且容易被如此剧烈的碰撞摧毁，这就造成了在L-CDM范式下观察到的薄盘比例与其存活率之间的一个关键矛盾。 在这里我们表明，在它们的祖先中观察到的高比例合并现象只是表面现象，在使用对合并过程所有阶段都敏感的形态动力学观测时，这一现象得到了解决。这提供了一种缩小星系合并率观测估计的新方法，并与最先进的L-CDM半经验模型的预测完美匹配，无需特别调整。这些结果意味着本地一半的薄盘并没有幸存下来，而是实际上在过去的九十亿年内，也就是宇宙寿命的三分之二时间内，经过一次富含气体的重大合并后重新形成。这强调了研究如何在比之前认为更活跃的合并历史的晕中形成薄盘的重要性，并调查当地盘重新形成时的气体储库的起源。