Mapping Extremely Low Metallicity Galaxies to Redshift One
Mapping Extremely Low Metallicity Galaxies to Redshift One
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DOI：
10.1086/521333
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发表时间：
2007-10
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影响因子：
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通讯作者：
Y. Kakazu;L. Cowie;E. Hu
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文献类型：
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作者：
Y. Kakazu;L. Cowie;E. Hu
本文描述了对EW（Hβ）≥ 30 nm的超强发射线星系（USELs）进行窄带搜索的结果。使用斯巴鲁SuprimeCam在8150和9140 <$m处的两个~120 <$m过滤器进行了一次半平方度的调查，共发现了542个候选星系。用Keck II DEIMOS对候选样本中随机选取的天体进行的后续光谱学研究表明，它们由[O III] λ5007-、[O II] λ3727-和Hα-选择的中等红移（z < 1）强发射线星系和高红移（z <5）Lyα-发射星系组成。我们确定了USELs的Hβ光度函数和星星形成密度，其值为z = 0-1时紫外连续天体的5%-10%，表明它们对应于星系形成过程中的一个主要时期。许多USEL显示出温度敏感的[O III] λ4363极光线，大约有十几个具有满足极端贫金属星系（XMPG）标准的氧丰度。这些XMPG是目前已知的最遥远的。我们的XMPG高产率表明，窄带方法是一个强大的方法来找到这样的群体。此外，在我们的样本中测量到的最低金属丰度接近于在本地星系中发现的最低金属丰度[12 + log（O/H）~ 7.1]，尽管我们需要更深的光谱来尽量减少误差。几个USEL的HST ACS图像表现出广泛的形态，从相对紧凑的高表面亮度的对象非常分散的低表面亮度的。USELs的光度、金属丰度和星星形成率与强发射体是启动的中等质量星系相一致，这些星系将演变成更正常的星系，并表明星系仍在z < 1的相对化学原始的位置形成。
We describe the results of a narrowband search for ultrastrong emission line galaxies (USELs) with EW(Hβ) ≥ 30 Å. A total of 542 candidate galaxies are found in a one-half square degree survey using two ~120 Å filters centered at 8150 and 9140 Å with Subaru SuprimeCam. Follow-up spectroscopy for randomly selected objects in the candidate sample with Keck II DEIMOS shows that they consist of [O III] λ5007-, [O II] λ3727-, and Hα-selected strong emission line galaxies at intermediate redshift (z < 1) and Lyα-emitting galaxies at high redshift (z ≫ 5). We determine the Hβ luminosity functions and the star formation density of the USELs, which is 5%-10% of the value found from ultraviolet continuum objects at z = 0-1, suggesting that they correspond to a major epoch in the galaxy formation process at these redshifts. Many of the USELs show the temperature-sensitive [O III] λ4363 auroral lines, and about a dozen have oxygen abundances satisfying the criteria of extremely metal-poor galaxies (XMPGs). These XMPGs are the most distant known today. Our high yield rate of XMPGs suggests that the narrowband method is a powerful way to find such populations. Moreover, the lowest metallicity measured in our sample is close to the minimum metallicity found in local galaxies [12 + log(O/H) ~ 7.1], although we need deeper spectra to minimize the errors. HST ACS images of several USELs exhibit widespread morphologies from relatively compact high surface brightness objects to very diffuse low surface brightness ones. The luminosities, metallicities, and star formation rates of USELs are consistent with the strong emitters being start-up intermediate-mass galaxies that will evolve into more normal galaxies and suggest that galaxies are still forming in relatively chemically pristine sites at z < 1.