Systematic Search for Galaxies in the Early Universe and their Nature

在两个区域对红移约5的星系(宇宙年龄约为1 Gyr)进行了大规模的系统观测，发现了约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的紫外光度函数(LF)。当我们将其与z=3，4(I)时的结果进行比较时，结果表明，在明亮的部分几乎没有演化，但在较弱的部分有轻微的演化。宇宙在z~5处的恒星形成率密度比z=3和z=4的宇宙恒星形成率密度小，但该时期的恒星形成活动仍然很高。对于亚样，我们得到了UV光谱。我们不仅可以证实红移，而且我们还发现Lyα的发射强度总体上很弱。我们还发现星际金属吸收线相对较强，这表明即使在~1Gyr(II)的宇宙年龄也存在一定程度的化学演化。此外，发射的等效宽度可能取决于它们的UV光度(III)。这表明Lyα发射体是微弱的Lyman Break星系的一个子类。得到了部分样品的静止标架光谱能量分布，并用光谱演化模型进行了拟合，估算了它们的消光年龄和消光量。我们还发现缺少蓝色发光星系(IV)。对Lyman Break星系的星系团性质的分析表明，其关联长度大于红移较低时的关联长度，支持星系在密度较高的区域较早形成的假设。在z~5时，发光星系具有较大的关联长度(V)。此外，我们将我们的星表与X射线源星表进行了交叉关联，发现了两到四个新的对应物。我们还对X射线成像数据进行了叠加分析，但没有检测到明显的信号。我们的结果(I)-(V)表明，在密度较高的区域，更多的大质量星系形成得更早。

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.