The Metallicity of Intergalactic Gas in Cosmic Voids
The Metallicity of Intergalactic Gas in Cosmic Voids
复制标题
宇宙空洞中星系际气体的金属丰度
DOI：
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发表时间：
2007
期刊：
影响因子：
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通讯作者：
M. Giroux
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文献类型：
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作者：
J. Stocke;C. Danforth;J. Shull;S. Penton;M. Giroux
我们利用哈勃STIS和FUSE的明亮活动星系核的紫外光谱档案来识别附近（z ≤ 0.1）空洞中的星系际Lyα吸收体。从651个Lyα吸收体的母样本中，我们确定了61个“空洞吸收体”，它们位于距离最近的L* 或更亮星系>1.4 h Mpc的位置。在高质量（S/N > 10）光谱中在三条诊断金属线（O VI λ1032，C IV λ1548，Si III λ1206）的位置处搜索金属吸收，我们使用像素共添加技术在任何单个吸收体或任何吸收体组中均未检测到金属线。利用四种N > 1014 cm-2的强Lyα吸收体设定了空隙中金属线吸收的最佳极限，3 σ等效宽度极限范围为8 mN（O VI）至7-15 mN（C IV）和4-10 mN（Si III）。光电离模型产生的金属丰度极限Z < 10-1.8±0.4 Z，来自未检测到的C IV和O VI，比在z < 0.1时在Lyα/O VI吸收体中观察到的低约6倍。虽然空洞的Lyα吸收体可能是原始的物质，但需要相当深的光谱才能排除早期星星形成的爆发所产生的普遍金属丰度底，而空洞中没有随后的星星形成。从这些低z结果和在z = 3-5的类似搜索中得出的最一致的结论是，自z ~ 3以来，星系细丝的平均IGM金属丰度增加了30-100倍。
We have used the Hubble STIS and FUSE archives of ultraviolet spectra of bright AGNs to identify intergalactic Lyα absorbers in nearby (z ≤ 0.1) voids. From a parent sample of 651 Lyα absorbers, we identified 61 "void absorbers" located >1.4 h Mpc from the nearest L* or brighter galaxy. Searching for metal absorption in high-quality (S/N > 10) spectra at the location of three diagnostic metal lines (O VI λ1032, C IV λ1548, Si III λ1206), we detected no metal lines in any individual absorber, or in any group of absorbers using pixel co-addition techniques. The best limits on metal-line absorption in voids were set using four strong Lyα absorbers with N > 1014 cm-2, with 3 σ equivalent-width limits ranging from 8 mÅ (O VI) to 7-15 mÅ (C IV) and 4-10 mÅ (Si III). Photoionization modeling yields metallicity limits Z < 10-1.8±0.4 Z☉ from nondetections of C IV and O VI, some ~6 times lower than those seen in Lyα/O VI absorbers at z < 0.1. Although the void Lyα absorbers could be pristine material, considerably deeper spectra are required to rule out a universal metallicity floor produced by bursts of early star formation, with no subsequent star formation in the voids. The most consistent conclusion derived from these low-z results and similar searches at z = 3-5 is that galaxy filaments have increased their mean IGM metallicity by factors of 30-100 since z ~ 3.