The Las Campanas Infrared Survey — V. Keck spectroscopy of a large sample of extremely red objects
The Las Campanas Infrared Survey — V. Keck spectroscopy of a large sample of extremely red objects
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DOI：
10.1111/j.1365-2966.2005.09191.x
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发表时间：
2005-05
影响因子：
4.8
通讯作者：
M. Doherty;A. Bunker;R. Ellis;Patrick J. McCarthy
中科院分区：
文献类型：
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作者：
M. Doherty;A. Bunker;R. Ellis;Patrick J. McCarthy
我们提出了深凯克光谱，使用深度成像多目标摄谱仪和低分辨率成像光谱仪摄谱仪，一个大的和代表性的样本67个极红物体（ERO）H = 20.5在三个领域（SSA 22，钱德拉深场南和NTT深场）从拉斯坎帕纳斯红外巡天（LCIRS）。使用本系列早期论文中采用的颜色切割（I-H）> 3.0（织女星星等），我们验证了这种选择对于定位和研究遥远的老源的效率。光谱红移被确定为44个来源，其中只有两个是污染的低质量恒星。当考虑到不完整性时，光谱红移分布与之前基于光度数据预测的结果非常吻合。我们的光谱具有足够的质量，我们可以解决z > 0.8 ERO人口的性质和均匀性的重要问题。一个占主导地位的老恒星人口推断为75%，我们的光谱样本，一个更高的分数比看到的更小，更完整的样本与更广泛的光度选择标准（如R-K）。然而，只有28%的光谱没有证据表明最近的星星形成活动，如预期的严格被动演变的人口。我们超过30%的吸收线光谱是“E+A”型的，具有显著的巴耳末吸收，平均而言，在过去的十亿年中，质量增长了5- 15%。我们使用我们的光谱红移，以改善早期的估计，这个人口的空间聚类，以及了解显着的字段到字段的变化。我们的光谱学使我们能够在Chandra深场南部的z = 1.22处精确定位一个非线性结构。总的来说，我们的研究表明，ERO人口的大部分是一个既定的人口集群的大质量星系进行间歇性活动与持续增长的红移间隔0.8 < z < 1.6。
We present deep Keck spectroscopy, using the Deep Imaging Multi-Object Spectrograph and the Low-Resolution Imaging Spectrometer spectrographs, of a large and representative sample of 67 extremely red objects (EROs) to H = 20.5 in three fields (SSA22, Chandra Deep Field South and NTT Deep Field) drawn from the Las Campanas Infrared Survey (LCIRS). Using the colour cut (I - H) > 3.0 (Vega magnitudes) adopted in earlier papers in this series, we verify the efficiency of this selection for locating and studying distant old sources. Spectroscopic redshifts are determined for 44 sources, of which only two are contaminating low-mass stars. When allowance is made for incompleteness, the spectroscopic redshift distribution closely matches that predicted earlier on the basis of photometric data. Our spectra are of sufficient quality that we can address the important question of the nature and homogeneity of the z > 0.8 ERO population. A dominant old stellar population is inferred for 75 per cent of our spectroscopic sample, a higher fraction than that seen in smaller, less complete samples with broader photometric selection criteria (e.g. R - K). However, only 28 per cent have spectra with no evidence of recent star formation activity, such as would be expected for a strictly passively evolving population. More than ∼30 per cent of our absorption-line spectra are of the 'E+A' type with prominent Balmer absorption consistent, on average, with mass growth of 5-15 per cent in the past gigayear. We use our spectroscopic redshifts to improve earlier estimates of the spatial clustering of this population as well as to understand the significant field-to-field variation. Our spectroscopy enables us to pinpoint a filamentary structure at z = 1.22 in the Chandra Deep Field South. Overall, our study suggests that the bulk of the ERO population is an established population of clustered massive galaxies undergoing intermittent activity consistent with continued growth over the redshift interval 0.8 < z < 1.6.