TRACING THE COSMIC METAL EVOLUTION IN THE LOW-REDSHIFT INTERGALACTIC MEDIUM
TRACING THE COSMIC METAL EVOLUTION IN THE LOW-REDSHIFT INTERGALACTIC MEDIUM
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追踪低红移星系间介质中的宇宙金属演化
DOI：
10.1088/0004-637x/796/1/49
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发表时间：
2014
期刊：
影响因子：
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通讯作者：
E. Tilton
中科院分区：
文献类型：
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作者：
J. Michael Shull;C. Danforth;E. Tilton
使用哈勃太空望远镜上的宇宙起源摄谱仪，我们测量了低红移 (z ≤ 0.4) 星系间介质 (IGM) 中六种离子 (C iii、C iv、Si iii、Si iv、N v 和 O vi) 的丰度。从 z ≈ 5.5 到现在，C iv 和 Si iv 的丰度都增加了 ∼10 倍。我们推导出离子质量密度，ρion == Ωionρcr，其中 Ωion 表示相对于闭合密度。我们的质量丰度比模型 (Si iii/Si iv) 、 (C iii/C iv) 和 与光电离参数 log U = −1.5 ± 0.4、氢光电离率 ΓH = (8 ± 2) × 10−14 s−1 (z < 0.4 时) 和比强度 I0 = (3 ± 1) × 一致10−23 erg cm−2 s−1 Hz−1 sr−1 在莱曼极限。 C 和 Si 的一致电离校正缩放至电离光子通量 Φ0 = 104 cm−2 s−1、重子超密度 Δb ≈ 200 ± 50 和“α 增强”（Si/C 增强至其太阳比的三倍）。我们将这些金属丰度与碳 (C v) 和硅 (Si v、Si vi 和 Si vii) 的较高光电离态的预期 IGM 富集度和丰度进行比较。我们的电离模型推断，在由 C 和 Si 离子追踪的光离子化 Lyα 森林中，IGM 金属密度为 (5.4 ± 0.5) × 105 M☉ Mpc−3，在由 O vi 追踪的较热气体中，IGM 金属密度为 (9.1 ± 0.6) × 105 M☉ Mpc−3。结合两相，IGM 中的重元素的质量密度为 ρZ = (1.5 ± 0.8) × 106 M☉ Mpc−3 或 ΩZ ≈ 10−5。这代表了 (6 ± 2) × 108 M☉ Mpc−3 集成恒星形成过程中产生的金属的 10% ± 5%，产量 ym = 0.025 ± 0.010。低红移缺失的金属可能存在于星系内以及星系晕和环绕星系介质中未检测到的电离气体中。
Using the Cosmic Origins Spectrograph aboard the Hubble Space Telescope, we measured the abundances of six ions (C iii, C iv, Si iii, Si iv, N v, and O vi) in the low-redshift (z ⩽ 0.4) intergalactic medium (IGM). Both C iv and Si iv have increased in abundance by a factor of ∼10 from z ≈ 5.5 to the present. We derive ion mass densities, ρion ≡ Ωionρcr, with Ωion expressed relative to the closure density. Our models of mass-abundance ratios, (Si iii/Si iv) , (C iii/C iv) , and , are consistent with the photoionization parameter log U = −1.5 ± 0.4, hydrogen photoionization rate ΓH = (8 ± 2) × 10−14 s−1 at z < 0.4, and specific intensity I0 = (3 ± 1) × 10−23 erg cm−2 s−1 Hz−1 sr−1 at the Lyman limit. Consistent ionization corrections for C and Si are scaled to an ionizing photon flux Φ0 = 104 cm−2 s−1, baryon overdensity Δb ≈ 200 ± 50, and “alpha-enhancement” (Si/C enhanced to three times its solar ratio). We compare these metal abundances to the expected IGM enrichment and abundances in higher photoionized states of carbon (C v) and silicon (Si v, Si vi, and Si vii). Our ionization modeling infers IGM metal densities of (5.4 ± 0.5) × 105 M☉ Mpc−3 in the photoionized Lyα forest traced by the C and Si ions and (9.1 ± 0.6) × 105 M☉ Mpc−3 in hotter gas traced by O vi. Combining both phases, the heavy elements in the IGM have mass density ρZ = (1.5 ± 0.8) × 106 M☉ Mpc−3 or ΩZ ≈ 10−5. This represents 10% ± 5% of the metals produced by (6 ± 2) × 108 M☉ Mpc−3 of integrated star formation with yield ym = 0.025 ± 0.010. The missing metals at low redshift may reside within galaxies and in undetected ionized gas in galactic halos and circumgalactic medium.