Discovery of Protoclusters at z ∼ 3.7 and 4.9: Embedded in Primordial Superclusters
Discovery of Protoclusters at z ∼ 3.7 and 4.9: Embedded in Primordial Superclusters
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DOI：
10.3847/1538-4357/ab5e85
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发表时间：
2019-12
期刊：
影响因子：
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通讯作者：
J. Toshikawa;M. Malkan;N. Kashikawa;R. Overzier;H. Uchiyama;K. Ota;S. Ishikawa;Kei Ito
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文献类型：
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作者：
J. Toshikawa;M. Malkan;N. Kashikawa;R. Overzier;H. Uchiyama;K. Ota;S. Ishikawa;Kei Ito
我们对加拿大-法国-夏威夷望远镜遗产巡天深场中g-和r-dropout星系的三个超密集区域进行了后续光谱分析，发现了z = 4.898和3.721的两个新的原星团和z = 3.834的一个可能的原星团。z = 3.721的原星团与先前发现的z = 3.675的原星团重叠。这两个原星团的红移距离为Δz = 0.05，略大于典型的原星团。因此，如果它们不是bbb1015 M☉光晕的祖先，它们将成长为像超星团一样位置紧密的独立光晕。另一个位于z = 4.898的原星团也被较小的星系群所包围。这些系统包括原星团和邻近星团，被认为是超星团的早期阶段。我们通过拟合三轴椭球体，量化了原星系团成员星系在z = 3.675和3.721处的空间分布，发现了一个初步的差异：一个呈薄饼状，而另一个呈丝状。这可能表明这两个原星团处于不同的形成阶段。我们研究了原星系团的红移与速度色散之间的关系，包括其他文献中的原星系团，以比较它们的动力学状态。虽然原星团的速度色散随红移没有明显的系统趋势，但在z = 2-6的红移范围内，速度色散偏大。这可以解释为星团形成的两个阶段，一个是星系的稳定吸积，另一个是星团大小的光晕之间的合并，这可能取决于周围的大尺度环境。
We have carried out follow-up spectroscopy on three overdense regions of g- and r-dropout galaxies in the Canada–France–Hawaii Telescope Legacy Survey Deep Fields, finding two new protoclusters at z = 4.898 and 3.721 and a possible protocluster at z = 3.834. The z = 3.721 protocluster overlaps with a previously identified protocluster at z = 3.675. The redshift separation between these two protoclusters is Δz = 0.05, which is slightly larger than the size of typical protoclusters. Therefore, if they are not the progenitors of a >1015 M☉ halo, they would grow into closely located independent halos like a supercluster. The other protocluster at z = 4.898 is also surrounded by smaller galaxy groups. These systems including protoclusters and neighboring groups are regarded as the early phase of superclusters. We quantify the spatial distribution of member galaxies of the protoclusters at z = 3.675 and 3.721 by fitting triaxial ellipsoids, finding a tentative difference: one has a pancake-like shape, while the other is filamentary. This could indicate that these two protoclusters are in different stages of formation. We investigate the relation between redshift and the velocity dispersion of protoclusters, including other protoclusters from the literature, in order to compare their dynamical states. Although there is no significant systematic trend in the velocity dispersions of protoclusters with redshift, the distribution is skewed to higher velocity dispersion over the redshift range of z = 2–6. This could be interpreted as two phases of cluster formation, one dominated by the steady accretion of galaxies and the other by the merging between group-size halos, perhaps depending on the surrounding large-scale environments.