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arXiv 1003.1780astro-ph.CO
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星爆后[ OII ]的起源和高红移星系团中的红序星系

The Origin of [OII] in Post-Starburst and Red-Sequence Galaxies in High-Redshift Clusters

Brian C. Lemaux, Lori M. Lubin, Alice E. Shapley, Dale D. Kocevski, Roy R. Gal, Gordon K. Squires

摘要:

本文首次报道了Cl 1604超星系团和RX J1821.6+6827超星系团在z~0.82处的近红外光谱活动的结果,以研究团星系中[OII] 3727 A发射在高红移下的性质。在这两个星系的401个成员中,有131个星系有可检测到的[OII]发射,没有其他当前恒星形成的迹象,以及强烈的吸收特征,表明一个成熟的老年恒星星族。这些特征的组合表明,这些星系中[OII]发射的主要来源不是恒星形成的结果,而是由于LINER或Seyfert组件的存在。使用凯克II 10米望远镜上的NIRSPEC摄谱仪,有19个这样的星系被锁定,还有另外6个发射[OII]的星团成员,它们显示出正在形成恒星的其他迹象。在19个以吸收线为主的[OII]发射星系中,近一半(约47%)的[OII]与Ha的等效宽度比大于1,这是恒星形成星系的典型值。根据[NII]和Ha的发射线比率,这19个星系中的大多数(约68%)被归类为LINER/Seyfert,对于红色[OII]发射,吸收线占主导地位的星系增加到约85%。LINER/Seyfert星系的L([OII])/L(Ha)比值明显高于在恒星形成星系中观察到的比值,这表明[OII]在大部分高红移星系团成员中是一个很差的恒星形成指标。我们估计在高红移星系团中至少有20%的星系包含可以用线比揭示的LINER/Seyfert分量。我们还调查了这个人口的影响,对恒星形成率的星系团星系和后星爆分数,得出结论,LINER/Seyferts必须占如果这些数量是有意义的。

英文摘要:

We present the first results from a near-IR spectroscopic campaign of the Cl1604 supercluster at z~0.9 and the cluster RX J1821.6+6827 at z~0.82 to investigate the nature of [OII] 3727A emission in cluster galaxies at high redshift. Of the 401 members in the two systems, 131 galaxies have detectable [OII] emission with no other signs of current star-formation, as well as strong absorption features indicative of a well-established older stellar population. The combination of these features suggests that the primary source of [OII] emission in these galaxies is not the result of star-formation, but rather due to the presence of a LINER or Seyfert component. Using the NIRSPEC spectrograph on the Keck II 10-m telescope, 19 such galaxies were targeted, as well as six additional [OII]-emitting cluster members that exhibited other signs of ongoing star-formation. Nearly half (~47%) of the 19 [OII]-emitting, absorption-line dominated galaxies exhibit [OII] to Ha equivalent width ratios higher than unity, the typical value for star-forming galaxies. A majority (~68%) of these 19 galaxies are classified as LINER/Seyfert based on the emission-line ratio of [NII] and Ha, increasing to ~85% for red [OII]-emitting, absorption-line dominated galaxies. The LINER/Seyfert galaxies exhibit L([OII])/L(Ha) ratios significantly higher than that observed in populations of star-forming galaxies, suggesting that [OII] is a poor indicator of star-formation in a large fraction of high-redshift cluster members. We estimate that at least ~20% of galaxies in high-redshift clusters contain a LINER/Seyfert component that can be revealed with line ratios. We also investigate the effect this population has on the star formation rate of cluster galaxies and the post-starburst fraction, concluding that LINER/Seyferts must be accounted for if these quantities are to be meaningful.

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