Identification of the progenitors of rich clusters and member galaxies in rapid formation at z>2
Identification of the progenitors of rich clusters and member galaxies in rapid formation at z>2
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DOI：
10.1093/mnrasl/slu029
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发表时间：
2014-02
影响因子：
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通讯作者：
R. Shimakawa;T. Kodama;K. Tadaki;I. Tanaka;M. Hayashi;Y. Koyama
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文献类型：
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作者：
R. Shimakawa;T. Kodama;K. Tadaki;I. Tanaka;M. Hayashi;Y. Koyama
本文给出了用多目标红外相机和光谱仪(MOIRCS)在斯巴鲁望远镜上对射电星系周围的两个原星系团(PKS1138-262和USS1558-003)的近红外光谱测量结果。在由我们的窄带成像构建的HAE候选者中，我们已经确认了各自原星系团的27和36个HAE成员资格，成功率为我们观察到的目标的70%。每个星系团的大量光谱确认成员使我们第一次揭示了原始星系团在$z$$>；$2的详细运动结构。星系团显示出突出的亚结构，如团块、细丝和速度梯度，这表明它们仍处于快速构建过程中，以便在以后成长为丰富的星系团。我们还估计了团簇和子结构的动力学质量，假设它们的局域维里化。如果我们考虑典型的星系团质量增长历史，推断出的原星系团核心的质量($SIM$10${14}$M$\ODOT$)与当今最大质量星系团($\SIM$10${15}$M$\\ODOT$)的典型祖先是一致的。然后，我们计算了由动力学质量归一化的原星系团核心的积分恒星形成率，并与低红移子体进行了比较。我们看到星团核心的恒星形成活动显著增加，几乎增加了三个数量级，因为我们回到110亿年前；这是(1$+$$z$)$^6$。
We present the results of near-infrared spectroscopy of H$\alpha$ emitters (HAEs) associated with two protoclusters around radio galaxies (PKS1138-262 at $z$=2.2 and USS1558-003 at $z$=2.5) with Multi-Object Infrared Camera and Spectrograph (MOIRCS) on the Subaru telescope. Among the HAE candidates constructed from our narrow-band imaging, we have confirmed membership of 27 and 36 HAEs for the respective protoclusters, with a success rate of 70 per cent of our observed targets. The large number of spectroscopically confirmed members per cluster has enabled us for the first time to reveal the detailed kinematical structures of the protoclusters at $z$$>$2. The clusters show prominent substructures such as clumps, filaments and velocity gradients, suggesting that they are still in the midst of rapid construction to grow to rich clusters at later times. We also estimate dynamical masses of the clusters and substructures assuming their local virialization. The inferred masses ($\sim$10$^{14}$M$_\odot$) of the protocluster cores are consistent with being typical progenitors of the present-day most massive class of galaxy clusters ($\sim$10$^{15}$M$_\odot$) if we take into account the typical mass growth history of clusters. We then calculated the integrated star formation rates of the protocluster cores normalized by the dynamical masses, and compare these with lower redshift descendants. We see a marked increase of star-forming activities in the cluster cores, by almost three orders of magnitude, as we go back in time to 11 billion years ago; this scales as (1$+$$z$)$^6$.