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arXiv 0705.1145astro-ph
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Z~5处的Lyman破缺:静止标架UV谱II

Lyman Break Galaxies at z~5: Rest-frame UV Spectra II

Masataka Ando, Kouji Ohta, Ikuru Iwata, Masayuki Akiyama, Kentaro Aoki, Naoyuki Tamura

摘要:

本文介绍了利用Subaru望远镜上的暗天体照相机和摄谱仪在J 0053 +1234视场中对Lyman Break Galeries(LBG)在z~5处的光谱测量结果。在5个z' < 25.0等的亮候选天体中,有2个天体的Ly α发射和Ly α的连续谱凹陷短缩证实了它们的位置在z~5。这两个LBG的Ly α发射的电子波没有Ly α发射那么强而难以被探测到,其中一个LBG显示出强的低电离星际(LIS)金属吸收线。两个z' \geq为25.0等的暗天体也被证实在z~5,它们的光谱显示出与亮天体相反的强Ly α发射。这些结果表明,在明亮的LBG在z~5强的Ly α发射的不足,这在我们以前的文章中已经讨论过。结合我们以前在哈勃深场北(HDF-N)周围获得的z~5处的LBG光谱,我们制作了z~5处的UV发光(M_1400 \leq -21.5 mag)LBG的合成光谱。得到的光谱显示出弱的Ly α发射和强的LIS反射,这表明在z~5处的明亮LBG至少已经化学演化到~0.1太阳金属丰度。对于HDF-N区域的一部分样本,我们获得了近中红外数据,这些数据限制了这些物体的恒星质量。由LIS估算的恒星质量和金属丰度,虽然不确定性很大,但z~5的LBG的金属丰度往往低于z \lesssim 2的LBG。

英文摘要:

We present the results of spectroscopy of Lyman Break Galaxies (LBGs) at z~5 in the J0053+1234 field with the Faint Object Camera and Spectrograph on the Subaru telescope. Among 5 bright candidates with z' < 25.0 mag, 2 objects are confirmed to be at z~5 from their Ly alpha emission and the continuum depression shortward of Ly alpha. The EWs of Ly alpha emission of the 2 LBGs are not so strong to be detected as Ly alpha emitters, and one of them shows strong low-ionized interstellar (LIS) metal absorption lines. Two faint objects with z' \geq 25.0 mag are also confirmed to be at z~5, and their spectra show strong Ly alpha emission in contrast to the bright ones. These results suggest a deficiency of strong Ly alpha emission in bright LBGs at z~5, which has been discussed in our previous paper. Combined with our previous spectra of LBGs at z~5 obtained around the Hubble Deep Field-North (HDF-N), we made a composite spectrum of UV luminous (M_1400 \leq -21.5 mag) LBGs at z~5. The resultant spectrum shows a weak Ly alpha emission and strong LIS absorptions which suggests that the bright LBGs at z~5 have chemically evolved at least to ~0.1 solar metallicity. For a part of our sample in the HDF-N region, we obtained near-to-mid infrared data, which constraint stellar masses of these objects. With the stellar mass and the metallicity estimated from LIS absorptions, the metallicities of the LBGs at z~5 tend to be lower than those of the galaxies with the same stellar mass at z \lesssim 2, although the uncertainty is very large.

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