z~0.4组的形态组成：S0形成的位点
Morphological Composition of z~0.4 groups: The site of S0 formation
摘要：
低红移宇宙（z<~0.5）并不是一个沉闷的地方。过程导致抑制恒星形成和形态转变是普遍的：这是特别明显的，在戏剧性的好转，在星系团中的S 0型星系的分数。然而，到目前为止，形成的过程和环境仍然不明。我们提出了一个基于HST的星系在红移空间选择组和场环境中的z~0.4的形态分析。在固定光度下，组包含比较低密度场高得多的S 0分数，置信度>99.999%。事实上，组中的SO分数至少与z~0.4的簇和X射线选择的组一样高，其具有更明亮的组内介质（IGM）。在固定光度下，在距离群中心>=0.3Mpc处有97%的置信度的S 0，这告诉我们形成并不局限于群核心，甚至可能避免群核心。与发出明亮X射线的IGM的相互作用对宇宙中大多数S 0的形成并不重要。与S 0 s不同的是，在固定光度下，椭圆星系在星系群中的比例与视场相似，而最亮的椭圆星系在朝向星系群中心的方向上被强烈增强（>99.999%置信度，在0.3Mpc范围内）。我们的结论是，集团和子集团的环境必须占主导地位的S 0星系的形成，和未成年人合并，星系骚扰和潮汐相互作用是最有可能负责的机制。这不仅对推断的星系团的预处理有影响，而且对星系的全局形态和恒星形成预算也有影响：随着等级聚类的进展，更多的星系将在进入星系团环境时经历这些转变。
英文摘要：
The low redshift Universe (z<~0.5) is not a dull place. Processes leading to the suppression of star formation and morphological transformation are prevalent: this is particularly evident in the dramatic upturn in the fraction of S0-type galaxies in clusters. However, until now, the process and environment of formation has remained unidentified. We present a HST-based morphological analysis of galaxies in the redshift-space selected group and field environments at z~0.4. Groups contain a much higher fraction of S0s at fixed luminosity than the lower density field, with >99.999% confidence. Indeed the S0 fraction in groups is at least as high as in z~0.4 clusters and X-ray selected groups, which have more luminous Intra Group Medium (IGM). An 97% confident excess of S0s at >=0.3Mpc from the group centre at fixed luminosity, tells us that formation is not restricted to, and possibly even avoids, the group cores. Interactions with a bright X-ray emitting IGM cannot be important for the formation of the majority of S0s in the Universe. In contrast to S0s, the fraction of elliptical galaxies in groups at fixed luminosity is similar to the field, whilst the brightest ellipticals are strongly enhanced towards the group centres (>99.999% confidence within 0.3Mpc). We conclude that the group and sub-group environments must be dominant for the formation of S0 galaxies, and that minor mergers, galaxy harassment and tidal interactions are the most likely responsible mechanisms. This has implications not only for the inferred pre-processing of cluster galaxies, but also for the global morphological and star formation budget of galaxies: as hierarchical clustering progresses, more galaxies will be subject to these transformations as they enter the group environment.
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