退休星系能模仿活动星系吗？斯隆数字巡天（Sloan Digital Sky Survey）
Can retired galaxies mimic active galaxies? Clues from the Sloan Digital Sky Survey
摘要：
恒星形成星系和活动星系的分类通常是在（[O III]/H β，[N II]/H α）平面上进行的。斯隆数字巡天（SDSS）显示，在这个平面上，星系的分布看起来像海鸥的两只翅膀。右翼的星系团被称为塞弗特/LINER，导致星系中的非恒星活动是一种非常普遍的现象。在这里，我们认为右翼的大部分系统实际上可能是停止形成恒星的星系。这些“退休”星系中的电离作用是由热的后AGB恒星和白矮星产生的。我们的论证是基于一个恒星星族分析的星系，通过我们的星光代码和光电离模型，使用莱曼连续辐射预测这个人口。然而，可以用这种方式解释的LINER星系的比例是不确定的。我们进一步展示了观测选择效应如何解释右翼的形状。我们的研究表明，核活动可能并不像想象的那样普遍。如果退休星系确实可以解释海鸥右翼的很大一部分，那么根据SDSS数据推断的一些关于星系核活动的工作将不得不进行修订。
英文摘要：
The classification of galaxies as star forming or active is generally done in the ([O III]/Hbeta, [N II]/Halpha) plane. The Sloan Digital Sky Survey (SDSS) has revealed that, in this plane, the distribution of galaxies looks like the two wings of a seagull. Galaxies in the right wing are referred to as Seyfert/LINERs, leading to the idea that non-stellar activity in galaxies is a very common phenomenon. Here, we argue that a large fraction of the systems in the right wing could actually be galaxies which stopped forming stars. The ionization in these "retired" galaxies would be produced by hot post-AGB stars and white dwarfs. Our argumentation is based on a stellar population analysis of the galaxies via our STARLIGHT code and on photoionization models using the Lyman continuum radiation predicted for this population. The proportion of LINER galaxies that can be explained in such a way is however uncertain. We further show how observational selection effects account for the shape of the right wing. Our study suggests that nuclear activity may not be as common as thought. If retired galaxies do explain a large part of the seagull's right wing, some of the work concerning nuclear activity in galaxies, as inferred from SDSS data, will have to be revised.
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