A LARGE NUMBER OF z > 6 GALAXIES AROUND A QSO AT z = 6.43: EVIDENCE FOR A PROTOCLUSTER?
A LARGE NUMBER OF z > 6 GALAXIES AROUND A QSO AT z = 6.43: EVIDENCE FOR A PROTOCLUSTER?
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QSO 周围 z = 6.43 处有大量 z > 6 个星系：原星系团的证据？
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发表时间：
2010
期刊：
影响因子：
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通讯作者：
R. Overzier
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文献类型：
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作者：
Y. Utsumi;T. Goto;N. Kashikawa;S. Miyazaki;Y. Komiyama;H. Furusawa;R. Overzier
类星体一直被认为对追踪早期宇宙中高度偏向的区域非常重要，今天的大质量星系和星系团就是从这些区域形成的。虽然已经在2<；z<；5的类星体周围发现了密度过高的恒星形成星系，但在z>；6的类星体周围发现过多星系聚集的理由就不那么清楚了。哈勃太空望远镜(HST)之前的研究报告称，在一些类星体领域探测到了微弱的遗失星系的小范围过剩，但这些调查探测到的是类星体周围相对较小的区域。为了解决这个问题，我们用SuPrime-Cam(34‘×27’)的大视场观测到了z=6.4的最远的类星体。新安装的红敏全耗尽CCD使我们能够更有效地选择z∼为6.4时的莱曼破裂星系(LBG)。我们在类星体场中发现了7个LBG，而在比较场中只有1个。如果没有光谱确认和额外的控制场，这种明显过剩的重要性很难量化。当一个人预计有4个天体时，发现7个天体的泊松概率是∼的10%，而在一个场中发现7个天体而在另一个场中只发现1个天体的概率不到0.4%，这表明类星体场相对于控制场来说明显过于密集。这些结论得到了与宇宙学平滑粒子流体动力学模拟的比较，该模拟包括星系的更高阶团簇。我们发现了一些证据，证明LBG以类星体为中心呈环状分布，半径为∼3Mpc。在距离类星体2 MPC的范围内没有候选的LBG，即星系聚集在类星体周围，但似乎避开了正中心。这些结果表明，当定义在足够大的尺度上(即，大于HST/ACS点)时，类星体被嵌入在过密区域中。这表明类星体确实诞生在一个巨大的光晕中。星系的中心亏损可能表明：(1)来自类星体的强紫外线辐射抑制了其附近星系的形成，或者(2)离类星体最近的恒星形成主要是以一种模糊的模式发生的，而我们的UV选择忽略了这一点。
QSOs have been thought to be important for tracing highly biased regions in the early universe, from which the present-day massive galaxies and galaxy clusters formed. While overdensities of star-forming galaxies have been found around QSOs at 2 < z < 5, the case for excess galaxy clustering around QSOs at z > 6 is less clear. Previous studies with the Hubble Space Telescope (HST) have reported the detection of small excesses of faint dropout galaxies in some QSO fields, but these surveys probed a relatively small region surrounding the QSOs. To overcome this problem, we have observed the most distant QSO at z = 6.4 using the large field of view of the Suprime-Cam (34′ × 27′). Newly installed red-sensitive fully depleted CCDs allowed us to select Lyman break galaxies (LBGs) at z ∼ 6.4 more efficiently. We found seven LBGs in the QSO field, whereas only one exists in a comparison field. The significance of this apparent excess is difficult to quantify without spectroscopic confirmation and additional control fields. The Poisson probability to find seven objects when one expects four is ∼10%, while the probability to find seven objects in one field and only one in the other is less than 0.4%, suggesting that the QSO field is significantly overdense relative to the control field. These conclusions are supported by a comparison with a cosmological smoothed particle hydrodynamics simulation which includes the higher order clustering of galaxies. We find some evidence that the LBGs are distributed in a ring-like shape centered on the QSO with a radius of ∼3 Mpc. There are no candidate LBGs within 2 Mpc from the QSO, i.e., galaxies are clustered around the QSO but appear to avoid the very center. These results suggest that the QSO is embedded in an overdense region when defined on a sufficiently large scale (i.e., larger than an HST/ACS pointing). This suggests that the QSO was indeed born in a massive halo. The central deficit of galaxies may indicate that (1) the strong UV radiation from the QSO suppressed galaxy formation in its vicinity or (2) that star formation closest to the QSO occurs mostly in an obscured mode that is missed by our UV selection.