COSMIC DUST IN Mg ii ABSORBERS
COSMIC DUST IN Mg ii ABSORBERS
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DOI：
10.1088/0004-637x/754/2/116
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发表时间：
2012-04
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影响因子：
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通讯作者：
B. M'enard;M. Fukugita
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文献类型：
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作者：
B. M'enard;M. Fukugita
Mg ii 吸收体引起背景类星体变红。我们测量了这种效应，并推断出存在于这些系统中的尘埃的宇宙密度为 Ω ≈ 2 × 10−6，以宇宙的临界密度为单位，这与银盘中发现的尘埃量相当，或者是推断的星系外存在的尘埃量的大约一半。我们还估计 Mg ii 云中的中性氢丰度为 Ω ≈ 1.5 × 10−4，大约相当于星系中恒星氢的 5%。这意味着 Mg ii 云的尘埃与气体质量比约为 1/100，这与正常星系的值相似。这将支持Mg ii云流出起源的假设，Mg ii云本质上没有恒星，因此没有尘埃来源。考虑到尘埃丰度意味着星系周围 Mg ii 吸收体的存在可以有效持续几个吉里。高红移吸收体使我们能够测量高达 900 Å 的静止框架消光曲线，在该曲线下，莱曼边缘的吸收在消光不透明度中超过了灰尘的散射。
Mg ii absorbers induce reddening on background quasars. We measure this effect and infer the cosmic density of dust residing in these systems to be Ω ≈ 2 × 10−6, in units of the critical density of the universe, which is comparable to the amount of dust found in galactic disks or about half the amount inferred to exist outside galaxies. We also estimate the neutral hydrogen abundance in Mg ii clouds to be Ω ≈ 1.5 × 10−4, which is approximately 5% of hydrogen in stars in galaxies. This implies a dust-to-gas mass ratio for Mg ii clouds of about 1/100, which is similar to the value for normal galaxies. This would support the hypothesis of the outflow origin of Mg ii clouds, which are intrinsically devoid of stars and hence have no sources of dust. Considerations of the dust abundance imply that the presence of Mg ii absorbers around galaxies lasts effectively for a few Gyr. High-redshift absorbers allow us to measure the rest-frame extinction curve to 900 Å, at which the absorption by the Lyman edge dominates over scattering by dust in the extinction opacity.