Gemini Deep Deep Survey. VI. Massive Hδ-strong Galaxies at z ≃ 1
Gemini Deep Deep Survey. VI. Massive Hδ-strong Galaxies at z ≃ 1
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双子座深海巡天。 z ≃ 1 处的大质量 Hδ 星系。
DOI：
10.1086/500005
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发表时间：
2005
期刊：
影响因子：
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通讯作者：
R. Murowinski
中科院分区：
文献类型：
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作者：
D. Le Borgne;R. Abraham;Kathryne J. Daniel;P. McCarthy;K. Glazebrook;S. Savaglio;D. Crampton;S. Juneau;R. Carlberg;Hsiao;R. Marzke;K. Roth;I. Jørgensen;R. Murowinski
我们发现，从z ~ 1.2到现在，具有强Hδ恒星吸收线的大质量星系的丰度急剧下降。这些“Hδ强”（HDS）星系在其星星形成活动中经历了最近的快速中断。结合来自Gemini Deep Deep和Sloan Digital Sky巡天的数据，制作质量匹配的样本（M ≥ 1010.2 M），分别有25个和50，255个星系，我们发现HDS阶段的星系比例从z = 1.2时的50%下降到今天的几个百分点。这种分数的减少是由于大质量HDS系统的数密度实际减少了2-4倍，加上大质量星系的数密度增加了约30%。我们表明，这个结果仅弱依赖于Hδ等效宽度（EW）定义HDS系统（如果大于4 μ m）所选择的阈值，并对应于（1 + z）2.5±0.7的演变。使用PÉGASE代码对高红移星族进行光谱合成研究，处理HδA、EW[O II]、Dn 4000和静止坐标系的颜色，支持这样的模型，即大质量HDS系统中的巴耳末吸收特征是星星形成的强烈事件的回声，这些事件在观测时期之前就消失了101 Gyr。z = 1.4-2的时代似乎对应于一个时间，在这个时间，大规模的星系是在从一个持续的星星形成的模式过渡到一个相对静止的模式与弱和罕见的星星形成插曲。我们认为，最有可能的地方遥远的大规模HDS星系的后代是被动演变的大规模星系在外地和小团体。
We show that there has been a dramatic decline in the abundance of massive galaxies with strong Hδ stellar absorption lines from z ~ 1.2 to the present. These "Hδ-strong" (HDS) galaxies have undergone a recent and rapid break in their star formation activity. Combining data from the Gemini Deep Deep and Sloan Digital Sky surveys to make mass-matched samples (M⋆ > 1010.2 M☉; with 25 and 50,255 galaxies, respectively), we find that the fraction of galaxies in an HDS phase has decreased from about 50% at z = 1.2 to a few percent today. This decrease in fraction is due to an actual decrease in the number density of massive HDS systems by a factor of 2-4, coupled with an increase in the number density of massive galaxies by ~30%. We show that this result depends only weakly on the threshold chosen for the Hδ equivalent width (EW) to define HDS systems (if greater than 4 Å) and corresponds to a (1 + z)2.5±0.7 evolution. Spectral synthesis studies of the high-redshift population using the PÉGASE code, treating HδA, EW[O II], Dn4000, and rest-frame colors, favor models in which the Balmer absorption features in massive HDS systems are the echoes of intense episodes of star formation that faded ≃1 Gyr prior to the epoch of observation. The z = 1.4-2 epoch appears to correspond to a time at which massive galaxies are in transition from a mode of sustained star formation to a relatively quiescent mode with weak and rare star formation episodes. We argue that the most likely local descendants of the distant massive HDS galaxies are passively evolving massive galaxies in the field and small groups.