红色序列和后喷星星系 [OII] 辐射的起源

我们利用 SDSS DR4 的光谱研究具有红色初稳颜色的星系的辐射线特性。检测到超过一半的红色星系中存在辐射线。我们关注两种常用于作为星系形成率指示器的辐射线：Ha 6563 和 [OII] 3727。[OII]/Ha 比率在完整 SDSS 样本中存在强烈二元性，这与红色颜色的二元性 closely 对应。 nearly all of the line-emitting red galaxies have line ratios typical of various types of AGN -- most commonly LINERs, a small fraction of transition objects and, more rarely, Seyferts。 Only ~6% of red galaxies display star-forming line ratios。 A straight line in the [OII]-Ha equivalent width plane separates LINER-like galaxies from other categories。 Quiescent galaxies with no detectable emission lines and LINER-like galaxies combine to form a single, tight red sequence in color-magnitude-concentration space。 [OII] EWs in LINER- and AGN-like galaxies can be as large as in star-forming galaxies。 Thus, unless objects with AGN/LINER-like line ratios are excluded, [OII] emission cannot be used directly as a proxy for star formation rate。 Lack of [OII] emission is generally used to indicate lack of star formation when post-starburst galaxies are selected at high redshift。 Our results imply, however, that these samples have been cut on AGN properties as well as star formation, and therefore may provide seriously incomplete sets of post-starburst galaxies。 Furthermore, post-starburst galaxies identifed in SDSS by requiring minimal Ha EW generally exhibit weak but nonzero line emission with ratios typical of AGNs; few of them show residual star formation。 This suggests that most post-starbursts may harbor AGNs/LINERs。