E+A星系和GALEX紫外线过剩早型星系的基本面：揭示它们之间的密切联系
The Fundamental Planes of E+A galaxies and GALEX UV-excess early-type galaxies: Revealing their intimate connection
摘要：
强的Balmer吸收线和缺乏Ha和[OII]发射线表明E+As是后星暴系统。最近的研究表明，E+As可能会经历从“蓝色云”到“红色序列”的过渡，并最终迁移到红色序列ETG。这个假设的观测验证是确定介于E+As和红色序列之间的星系群。最近的研究结果与GALEX的大部分ETGs表现出紫外线过剩的RSF的标志的动机，我们调查的紫外线过剩的星系E+As的可能的连接。特别是，我们研究了从SDSS中选择的约1，000个E+As的最大样本和约20，000个形态选择的SDSS ETG与GALEX UV数据的FP标度关系。FP参数，结合恒星星族指标，揭示了一组特定的紫外线过量ETG之间的桥梁E+As和静止的红色星系。新发现的星系是以紫外线过剩但没有Ha辐射为特征的星暴后星系。这是“E+A”的概念概括，因为“E+A”定义中的巴耳末吸收线被替换为对RSF比巴耳末线敏感得多的紫外光学颜色。我们将这些紫外线过剩的星系称为“E+a”星系，代表椭圆（“E”）星系和少数A型（“a”）年轻恒星。这类星系要么是（1）经历过比在E+As中观测到的星爆弱的星系（1~10%的E+As，“温和的E+As”），要么是（2）被动演化的E+As在相当长一段时间前淬灭恒星形成后的产物（~1 Gyr，“老E+As”）。我们认为，后一种类型的E+A星系代表最近到达的红色序列的最后阶段的“E+A”到“红色早期型”的过渡。（节录）
英文摘要：
Strong Balmer absorption lines and the lack of Ha and [OII] emission lines signify that E+As are post-starburst systems. Recent studies suggest that E+As may undergo the transition from the `blue cloud' to the `red sequence' and eventually migrate to red sequence ETGs. An observational validation of this scenario is to identify the intervening galaxy population between E+As and the red-sequence. Motivated by recent findings with GALEX that a large fraction of ETGs exhibit UV-excess as a sign of RSF, we investigate the possible connection of the UV-excess galaxies to E+As. In particular, we examine the FP scaling relations of the largest sample of ~1,000 E+As selected from the SDSS and ~20,000 morphologically-selected SDSS ETGs with GALEX UV data. The FP parameters, combined with stellar population indicators, reveal a certain group of UV-excess ETGs that bridges between E+As and quiescent red galaxies. The newly identified galaxies are the post-starburst systems characterized by UV-excess but no Ha emission. This is a conceptual generalisation of "E+A", in that the Balmer absorption line in the "E+A" definition is replaced with UV-optical colours that are far more sensitive to RSF than the Balmer lines. We refer to these UV-excess galaxies as "E+a" galaxies, which stands for elliptical ("E") galaxies with a minority of A-type ("a") young stars. The species are either (1) galaxies that experienced starbursts weaker than those observed in E+As (1~10% of E+As, "mild E+As") or (2) the products of passively evolved E+As after quenching star formation quite a while ago (~1 Gyr, "old E+As"). We suggest that the latter type of E+a galaxies represents the most recent arrival to the red sequence in the final phase of the "E+A" to "red early-type" transition. (Abridged)
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