Deficiency of large equivalent width Lyα emission in luminous lyman break galaxies at z ∼ 5-6?
Deficiency of large equivalent width Lyα emission in luminous lyman break galaxies at z ∼ 5-6?
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DOI：
10.1086/505652
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发表时间：
2006-07-01
影响因子：
4.9
通讯作者：
Tamura, Naoyuki
中科院分区：
文献类型：
--
作者：
Ando, Masataka;Ohta, Kouji;Tamura, Naoyuki
我们报告了一个发光的莱曼断裂星系（LBGs）的缺陷，它们在z点的Ly α发射具有大的静止框架等效宽度（EWrest），类似于5-6。结合我们的LBGs光谱样本和来自文献的样本，我们发现发光的LBGs通常显示弱的Lya发射，而微弱的LBGs显示大范围的Ly α EWrest，并且往往具有强的（EWrest大于或接近20埃）Ly α发射；即，在发光lbg中存在强Lya发射的缺陷。似乎有一个阈值的紫外线亮度不足；M-1400 = -21.5 ~ -21.0等，接近或略亮于z点UV光度函数的M-*，类似于5和6。由于在微弱的LBGs中可以看到Ly α发射的大量EWrest，因此与LBGs相似的5 Lya发射体的z比值可能会随着UV亮度的变化而突然变化。如果Lya发射的微弱是由于尘埃吸收，那么这种缺陷表明，z = 5 - 6处发光的LBGs往往处于尘埃和化学进化程度更高的环境中，并且它们比微弱的LBGs更早开始形成恒星，尽管不能排除其他原因。
We report a deficiency of luminous Lyman break galaxies (LBGs) with a large rest-frame equivalent width (EWrest) of Ly alpha emission at z similar to 5-6. Combining our spectroscopic sample of LBGs at and those from the literature, we found that luminous LBGs at generally show weak Lya emissions, while faint LBGs show a wide range of Ly alpha EWrest and tend to have strong (EWrest greater than or similar to 20 angstrom) Ly alpha emissions; i. e., there is a deficiency of strong Lya emission in luminous LBGs. There seems to be a threshold UV luminosity for the deficiency; it is M-1400 = -21.5 to -21.0 mag, which is close to or somewhat brighter than the M-* of the UV luminosity function at z similar to 5 and 6. Since the large EWrest of Ly alpha emission can be seen among the faint LBGs, the ratio of z similar to 5 Lya emitters to LBGs may change rather abruptly with the UV luminosity. If the weakness of Lya emission is due to dust absorption, the deficiency suggests that luminous LBGs at z = 5 - 6 tend to be in dusty and more chemically evolved environments and that they begin star formation earlier than faint LBGs, although other causes cannot be ruled out.