The Low-z Intergalactic Medium. II. Lyβ, O VI, and C III Forest
The Low-z Intergalactic Medium. II. Lyβ, O VI, and C III Forest
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低 z 星际介质 Lyβ、O VI 和 C III 森林。
DOI：
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发表时间：
2005
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通讯作者：
J. Stocke
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作者：
C. Danforth;J. Shull;J. L. Rosenberg;J. L. Rosenberg;J. Stocke
我们展示了对低红移 (z < 0.3) 星系际介质 (IGM) 中的 H I、O VI 和 C III 吸收线进行大型调查的结果。我们从使用哈勃太空望远镜研究的 31 个 AGN 视线中的 171 条强 Lyα 吸收线 (Wλ ≥ 80 mÅ) 开始，并使用 FUSE 测量来自高阶莱曼线的相应吸收。高阶莱曼线用于通过生长曲线 (COG) 分析准确确定 N 和 b。我们发现每个列密度箱的 H I 吸收体数量呈幂律分布 d?/dN ∝ N，其中 β = 1.68 ± 0.11。我们分别在 129 个和 148 个潜在吸收体中对 O VI λλ1032 进行了 40 次检测，对 C III λ977 进行了 1038 次检测和 30 次检测。 C III 吸收体的柱密度分布为 β = 1.68 ± 0.04，与 β 相似，但不像 β = 2.2 ± 0.1 那样陡峭。根据吸收线频率，当 Wλ(C ) > 30 mÅ 时，d?/dz = 12，我们计算出典型的 IGM 吸收体尺寸 r0 ~ 400 kpc，类似于通过其他方式得出的尺度。 COG 导出的 b 值表明 H I 采样材料的 T < 105 K，与热 IGM 相不相容。通过计算具有一系列碰撞和光电离参数的 IGM 吸收体的 CLOUDY 模型网格，我们发现很难同时解释单相的 O VI 和 C III 观测结果。相反，观测需要多相 IGM，其中 H I 和 C III 出现在光离子化区域，而 O VI 主要通过冲击产生。根据多相比 N/N，我们推断 IGM 金属丰度为 ZC = 0.12 Z☉，类似于我们之前根据 O VI 估计的 ZO = 0.09 Z☉。
We present the results of a large survey of H I, O VI, and C III absorption lines in the low-redshift (z < 0.3) intergalactic medium (IGM). We begin with 171 strong Lyα absorption lines (Wλ ≥ 80 mÅ) in 31 AGN sight lines studied with the Hubble Space Telescope and measure corresponding absorption from higher order Lyman lines with FUSE. Higher order Lyman lines are used to determine N and b accurately through a curve-of-growth (COG) analysis. We find that the number of H I absorbers per column density bin is a power-law distribution, d?/dN ∝ N, with β = 1.68 ± 0.11. We made 40 detections of O VI λλ1032, 1038 and 30 detections of C III λ977 out of 129 and 148 potential absorbers, respectively. The column density distribution of C III absorbers has β = 1.68 ± 0.04, similar to β but not as steep as β = 2.2 ± 0.1. From the absorption-line frequency, d?/dz = 12 for Wλ(C ) > 30 mÅ, we calculate a typical IGM absorber size r0 ~ 400 kpc, similar to scales derived by other means. The COG-derived b-values show that H I samples material with T < 105 K, incompatible with a hot IGM phase. By calculating a grid of CLOUDY models of IGM absorbers with a range of collisional and photoionization parameters, we find it difficult to simultaneously account for the O VI and C III observations with a single phase. Instead, the observations require a multiphase IGM in which H I and C III arise in photoionized regions, while O VI is produced primarily through shocks. From the multiphase ratio N/N, we infer the IGM metallicity to be ZC = 0.12 Z☉, similar to our previous estimate of ZO = 0.09 Z☉ from O VI.