THE LACK OF INTENSE Lyα IN ULTRADEEP SPECTRA OF z = 7 CANDIDATES IN GOODS-S: IMPRINT OF REIONIZATION?
THE LACK OF INTENSE Lyα IN ULTRADEEP SPECTRA OF z = 7 CANDIDATES IN GOODS-S: IMPRINT OF REIONIZATION?
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Goods-S 中 z = 7 候选者的超深光谱中缺乏强烈的 Lyα：再电离的印记？
DOI：
10.1088/2041-8205/725/2/l205
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发表时间：
2010
期刊：
影响因子：
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通讯作者：
P. Santini
中科院分区：
文献类型：
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作者：
A. Fontana;E. Vanzella;L. Pentericci;M. Castellano;M. Giavalisco;A. Grazian;K. Boutsia;S. Cristiani;M. Dickinson;E. Giallongo;R. Maiolino;A. Moorwood;P. Santini
利用甚大望远镜（VLT）上FORS 2观测了7个在GOODS-S视场中从Hawk-I/VLT和WFC 3/HST成像中选出的z>6.5的莱曼break星系（LBG）候选星系的超深光谱。对于一个星系，我们探测到一条低显著性的发射线（S/N <$7），位于λ = 9691.5 ± 0.5 <$m，通量为3.4 × 10−18 erg cm−2 s−1。如果确定为Lyα，它将LBG放置在红移z = 6.972 ± 0.002处，其静止帧等效宽度EWrf = 13 μ m。使用蒙特卡罗模拟和2 < z < 6的保守EW分布函数，我们估计在信噪比大于10的情况下，在我们的数据中没有观测到星系的概率是10.2%，而在信噪比= 5的情况下，7个星系中只有1个星系被观测到的概率是10.4%，但这些概率可以小到10.10 −3，这取决于EW分布的细节。我们的结论是，要么是有相当一部分候选星系的红移不高，要么是某些物理机制在z>6.5时淬灭了星系中的Lyα发射，突然扭转了观测到的红移增加到z ≥ 6.5时强发射体比例增加的趋势。我们讨论的可能性，越来越中性的星系际介质是负责这种淬火。
We present ultradeep optical spectroscopy obtained with FORS2 on the Very Large Telescope (VLT) of seven Lyman-break galaxy (LBG) candidates at z>6.5 selected in the GOODS-S field from Hawk-I/VLT and WFC3/HST imaging. For one galaxy we detect a low significance emission line (S/N ⩽ 7), located at λ = 9691.5 ± 0.5 Å and with flux 3.4 × 10−18 erg cm−2 s−1. If identified as Lyα, it places the LBG at redshift z = 6.972 ± 0.002, with a rest-frame equivalent width EWrf = 13 Å. Using Monte Carlo simulations and conservative EW distribution functions at 2 < z < 6, we estimate that the probability of observing no galaxies in our data with S/N>10 is ≃2%, and that of observing only one galaxy out of seven with S/N = 5 is ≃4%, but these can be as small as ∼10−3, depending on the details of the EW distribution. We conclude that either a significant fraction of the candidates is not at high redshift or that some physical mechanism quenches the Lyα emission emerging from the galaxies at z>6.5, abruptly reversing the trend of the increasing fraction of strong emitters with increasing redshift observed up to z ∼ 6.5. We discuss the possibility that an increasingly neutral intergalactic medium is responsible for such quenching.