一个红移z ~ 10的候选星系及其在5亿年年龄时的快速变化
A candidate redshift z ~ 10 galaxy and rapid changes in that population at an age of 500 Myr
摘要：
在过去的十年中，对极高红移星系的研究已经产生了一个大样本，其中有超过6，000个星系存在于大爆炸后的9亿~ 20亿年（Myr）（红移6 > z > 3;参考文献1）。哈勃超深空望远镜（HUDF 09）的数据首次可靠地探测到了z ~ 8星系，这些星系与z ~ 8.2的伽马射线暴一起构成了迄今为止可靠报道的最早天体。对z ~ 7-8星系的观测表明，在z > 9-10时有大量的恒星形成。在这里，我们使用了整整两年的HUDF 09数据，对再电离时代中心的z ~ 10星系进行了超深搜索，距离大爆炸只有5亿年。我们不仅找到了一个可能的z ~ 10星系候选者，而且我们表明，无论源检测如何，此时的恒星形成率密度要比z ~ 8时的2亿年后小得多（~10%）。这表明星系在z ~ 10时的快速形成，因为星系的光度密度和体积密度从z ~ 8到z ~ 10都在增加。z ~ 10之前的1亿~ 2亿年显然是最早星系聚集的关键阶段。
英文摘要：
Searches for very-high-redshift galaxies over the past decade have yielded a large sample of more than 6,000 galaxies existing just 900-2,000 million years (Myr) after the Big Bang (redshifts 6 > z > 3; ref. 1). The Hubble Ultra Deep Field (HUDF09) data have yielded the first reliable detections of z ~ 8 galaxies that, together with reports of a gamma-ray burst at z ~ 8.2 (refs 10, 11), constitute the earliest objects reliably reported to date. Observations of z ~ 7-8 galaxies suggest substantial star formation at z > 9-10. Here we use the full two-year HUDF09 data to conduct an ultra-deep search for z ~ 10 galaxies in the heart of the reionization epoch, only 500 Myr after the Big Bang. Not only do we find one possible z ~ 10 galaxy candidate, but we show that, regardless of source detections, the star formation rate density is much smaller (~10%) at this time than it is just ~200 Myr later at z ~ 8. This demonstrates how rapid galaxy build-up was at z ~ 10, as galaxies increased in both luminosity density and volume density from z ~ 8 to z ~ 10. The 100-200 Myr before z ~ 10 is clearly a crucial phase in the assembly of the earliest galaxies.
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