解码SDSS早期星系的光谱：年龄和最近恒星形成的新指标
Decoding the spectra of SDSS early-type galaxies: New indicators of age and recent star formation
摘要：
本文对斯隆数字巡天（SDSS）中的早期星系样本进行了主成分分析（PCA），以推断它们恒星形成历史的差异。在前几个主成分（PC），我们研究了四个提供信息的恒星星族和速度色散。我们构造两个参数（eta和zeta）作为PC 1和PC 2的线性组合。我们发现zeta对最近的恒星形成最为敏感，而eta则强烈依赖于恒星星族的平均年龄。复合材料的eta分量的分布似乎是难以区分的高密度和低密度区域之间，而zeta参数的分布有一个显着的倾斜向较低的值在低密度区域的星系。这一结果表明，在低密度环境中的星系不太可能出现最近恒星形成的弱事件。相比之下，我们的高密度子样本中的大量星系-包括星系团（外部区域和中心）和星系团-在高金属丰度下经历了小但可检测的近期恒星形成，与最近针对希克森致密星系团和该领域的椭圆星系的估计一致（Ferreras等人）。
英文摘要：
(Abridged) We apply Principal Component Analysis (PCA) to a sample of early-type galaxies from the Sloan Digital Sky Survey (SDSS) in order to infer differences in their star formation histories. Out of the first few principal components (PC), we study four which give information about stellar populations and velocity dispersion. We construct two parameters (eta and zeta) as linear combinations of PC1 and PC2. We find zeta to be most sensitive to recent episodes of star formation, and eta to be strongly dependent on the average age of the stellar populations. The distribution of the eta component of the composites appear to be indistinguishable between high and low density regions, whereas the distribution of zeta parameters have a significant skew towards lower values for galaxies in low density regions. This result suggests that galaxies in lower density environments are less likely to present weak episodes of recent star formation. In contrast, a significant number of galaxies from our high density subsample -- which includes clusters (both outer regions and centres) and groups -- underwent small but detectable recent star formation at high metallicity, in agreement with recent estimates targeting elliptical galaxies in Hickson Compact Groups and in the field (Ferreras et al.).
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