Deep Spectroscopy of Systematically Surveyed Extended Lyα Sources at z ~ 3-5
Deep Spectroscopy of Systematically Surveyed Extended Lyα Sources at z ~ 3-5
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DOI：
10.1086/527282
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发表时间：
2007-05
期刊：
影响因子：
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通讯作者：
Tomoki Saito;K. Shimasaku;S. Okamura;M. Ouchi;M. Akiyama;Michitoshi Yoshida;Y. Ueda
中科院分区：
文献类型：
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作者：
Tomoki Saito;K. Shimasaku;S. Okamura;M. Ouchi;M. Akiyama;Michitoshi Yoshida;Y. Ueda
空间扩展的Lyα源是微弱的和/或致密的连续体，是极年轻（小于107年）的高红移星系的候选者。我们展示了在我们之前的研究中发现的18个这样的扩展Lyα源的中分辨率（R ~ 2000） VLT/VIMOS光谱。深度光谱分析表明，这18个天体都具有较大的等效宽度（EWs），在静止帧中超过100 Å。对于大约30%的样本（五个物体），我们在Lyα线的轮廓中发现了明显的不对称性。它们在红色一侧显示了宽翼发射成分，在Lyα线的蓝色一侧显示了一个尖锐的切断。这种不对称性经常出现在超风星系中，也与超风的理论预测相一致。事实上，其中一个在二维光谱中显示出系统的速度结构，表明存在超风活动。有8个天体（8/18 ~ 40%）具有非常大的EWs，超过200 Å （rest frame），并且没有明显的超风活动特征。如此大的EWs不能用中等年龄（100 - 107年）恒星群的光电离来解释，即使具有头重头轻的IMF或极低的金属丰度。这8个天体的Lyα线光度与速度宽度明显呈正相关。这表明这8个天体是在气体冷却阶段（冷吸积）形成星系的良好候选者。
Spatially extended Lyα sources that are faint and/or compact in continuum are candidates for extremely young (≲107 yr) galaxies at high redshifts. We present medium-resolution (R ∼ 2000) VLT/VIMOS spectroscopy of 18 such extended Lyα sources found in our previous study at z ∼ 3-5. The deep spectroscopy showed that all 18 objects have large equivalent widths (EWs), exceeding 100 Å in the rest frame. For about 30% of our sample (five objects), we identified conspicuous asymmetry in the profile of the Lyα line. They show broad wing emission components on the red side, and a sharp cutoff on the blue side of the Lyα line. Such asymmetry is often seen in superwind galaxies, and is also consistent with the theoretical prediction of superwinds. In fact, one of them shows systematic velocity structure in the two-dimensional spectrum, suggesting the existence of superwind activity. There are eight objects (8/18 ∼ 40% ) that have very large EWs, exceeding 200 Å (rest frame), and no clear signature of superwind activities. Such large EWs cannot be explained in terms of photoionization by a moderately old (>107 yr) stellar population, even with a top-heavy IMF or an extremely low metallicity. These eight objects clearly show a positive correlation between the Lyα line luminosity and the velocity width. This suggests that these eight objects are good candidates for forming galaxies in a gas-cooling phase (cold accretion).