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Systematic Search for Galaxies in the Early Universe and their Nature

系统搜索早期宇宙中的星系及其性质

基本信息

批准号：
15540233
负责人：
OHTA Kouji
金额：
$ 1.79万
依托单位：
Kyoto University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2003
资助国家：
日本
起止时间：
2003 至 2004
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-15540233/
关键词：
galaxies galaxy formation galaxy evolution Lyman break galaxies

项目摘要

Large systematic surveys for galaxies at redshift around 5 (cosmic age of 〜1 Gyr) were made in two fields, and found about 600 candidates. This is the largest sample in the world. Using the sample, we found the followings : We derived UV luminosity function(LF) of the galaxies with the highest accuracy. The resulting UVLF show an almost no evolution in the bright part, but a slight evolution in the fainter part when we compare it with those at z=3,4 (i). The cosmic star-formation rate density at z〜5 was turned out to be smaller than those at z=3 and 4, but the star-formation activity is still high in the era. For the subsample, we obtained UV spectra. We could confirm not only the redshifts, but also we found strength of Lyα emission is generally weak. We also found that interstellar metallic absorption lines were relatively strong, suggesting the presence of chemical evolution to some degree even at the cosmic age of 〜1Gyr(ii). Further, equivalent widths of the emissions may depend on UV luminosities of them (iii). This suggests that Lyα emitters are a subclass of the faint Lyman break galaxies. We obtain rest-frame spectral energy distributions of a part of the sample, and made fitting with spectral evolution model ; ages and amounts of dust extinction of them were estimated. We also found a lack of blue luminous galaxies (iv). Analysis of clustering property of Lyman break galaxies showed its correlation length was t larger than that at lower redshifts, supporting a scenario that galaxies formed earlier in the denser region. At z〜5, luminous galaxies tend to show a larger correlation length (v). In addition, we cross-correlated our catalog with X-ray source catalog and found two to four new counterparts. We also made stacking analysis with X-ray imaging data, but no significant signal was detected. Our results shown above (i)-(v) suggest that more massive galaxies formed earlier in the denser region.

在两个领域对红移约5（宇宙年龄约1 Gyr）的星系进行了大规模系统调查，发现了大约600个候选星系。这是世界上最大的样本。利用该样本，我们得到了精度最高的星系紫外光度函数（LF）。与z=3,4 (i)处相比，所得的UVLF在明亮部分几乎没有变化，但在较暗部分有轻微的变化。z ~ 5的宇宙恒星形成速率密度小于z=3和z= 4，但该时代的恒星形成活动仍然很高。对于子样品，我们获得了紫外光谱。我们不仅可以确认红移，而且还发现Lyα的发射强度一般较弱。我们还发现星际金属吸收线相对较强，表明即使在~ 1Gyr（ii）的宇宙年龄，也存在一定程度的化学演化。此外，辐射的等效宽度可能取决于它们的紫外光度（iii）。这表明Lyα发射体是暗淡的Lyman断裂星系的一个亚类。得到了部分样品的静帧光谱能量分布，并用光谱演化模型进行拟合；估计了它们的年龄和消尘量。我们还发现缺少蓝色发光星系（iv）。对莱曼断裂星系的聚类特性分析表明，它的相关长度大于低红移时的相关长度，支持了星系在密度较大区域形成较早的假设。在z ~ 5处，发光星系往往表现出较大的相关长度(v)。此外，我们将我们的星表与x射线源星表交叉比对，发现了2到4个新的对应星表。我们也对x射线成像数据进行了叠加分析，但未发现明显的信号。上面(i)-(v)的结果表明，更大质量的星系在密度更大的区域形成得更早。