SPECTROSCOPIC CONFIRMATION OF THREE z-DROPOUT GALAXIES AT z = 6.844–7.213: DEMOGRAPHICS OF Lyα EMISSION IN z ∼ 7 GALAXIES
SPECTROSCOPIC CONFIRMATION OF THREE z-DROPOUT GALAXIES AT z = 6.844–7.213: DEMOGRAPHICS OF Lyα EMISSION IN z ∼ 7 GALAXIES
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DOI：
10.1088/0004-637x/744/2/83
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发表时间：
2011-07
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通讯作者：
Y. Ono;M. Ouchi;B. Mobasher;M. Dickinson;K. Penner;K. Shimasaku;B. Weiner;J. Kartaltepe;K. Nakajima;H. Nayyeri;D. Stern;N. Kashikawa;H. Spinrad
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作者：
Y. Ono;M. Ouchi;B. Mobasher;M. Dickinson;K. Penner;K. Shimasaku;B. Weiner;J. Kartaltepe;K. Nakajima;H. Nayyeri;D. Stern;N. Kashikawa;H. Spinrad
我们提出了我们的超深凯克/DEIMOS光谱的z-dropout星系在斯巴鲁深场和大天文台起源深调查的北方领域的结果。对于11个物体中的3个，我们检测到在101 μm处的发射线，信噪比为100。这些谱线显示出高加权偏度值的不对称轮廓，与Lyα一致，产生红移z = 7.213、6.965和6.844。具体来说，我们确认z = 7.213对象在两个独立的DEIMOS运行不同的光谱配置。z = 6.965的天体是一个已知的Lyα发射体，IOK-1，我们改进的光谱在更高的分辨率下产生了一个强大的偏斜测量。这三个z-下降点的Lyα通量为3 × 10−17 erg s−1 cm−2，静止坐标系等效宽度EWLyα0 = 33-43 erg。基于最大的光谱样本43 z-dropouts，这是我们和以前的数据相结合，我们发现，Lyα发射星系（EWLyα0 > 25 <$）的比例很低，在z <$7; 17% ± 10%和24% ± 12%分别为明亮（MUV <$−21）和暗淡（MUV <$−19.5）星系。Lyα发射星系的比例从z = 6下降到z = 7，并且暗星系的下降幅度大于亮星系。这两个证据表明星系际介质中的中性氢含量从z = 6增加到z = 7，并且再电离从高密度环境到低密度环境进行，正如由内而外的再电离模型所建议的那样。
We present the results of our ultra-deep Keck/DEIMOS spectroscopy of z-dropout galaxies in the Subaru Deep Field and Great Observatories Origins Deep Survey's northern field. For 3 out of 11 objects, we detect an emission line at ∼1 μm with a signal-to-noise ratio of ∼10. The lines show asymmetric profiles with high weighted skewness values, consistent with being Lyα, yielding redshifts of z = 7.213, 6.965, and 6.844. Specifically, we confirm the z = 7.213 object in two independent DEIMOS runs with different spectroscopic configurations. The z = 6.965 object is a known Lyα emitter, IOK-1, for which our improved spectrum at a higher resolution yields a robust skewness measurement. The three z-dropouts have Lyα fluxes of 3 × 10−17 erg s−1 cm−2 and rest-frame equivalent widths EWLyα0 = 33–43 Å. Based on the largest spectroscopic sample of 43 z-dropouts, which is the combination of our and previous data, we find that the fraction of Lyα-emitting galaxies (EWLyα0 > 25 Å) is low at z ∼ 7; 17% ± 10% and 24% ± 12% for bright (MUV ≃ −21) and faint (MUV ≃ −19.5) galaxies, respectively. The fractions of Lyα-emitting galaxies drop from z ∼ 6 to 7 and the amplitude of the drop is larger for faint galaxies than for bright galaxies. These two pieces of evidence would indicate that the neutral hydrogen fraction of the intergalactic medium increases from z ∼ 6 to 7 and that the reionization proceeds from high- to low-density environments, as suggested by an inside-out reionization model.