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首页> 外文期刊>The Astrophysical journal >STIS OBSERVATIONS OF He II GUNN-PETERSON ABSORPTION TOWARD Q0302--003
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STIS OBSERVATIONS OF He II GUNN-PETERSON ABSORPTION TOWARD Q0302--003

机译：He II GUNN-PETERSON吸附对Q0302--003的STIS观察

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摘要

The ultraviolet spectrum (1145--1720 A) of the distant quasar Q0302--003 (z = 3.286) was observed at 1.8 A resolution .ith the Space Telescope Imaging Spectrograph aboard the Hubble Space Telescope. A total integration time of 23,280 s was obtained. The spectrum clearly delineates the Gunn-Peterson He II absorption trough, produced by He II Lyα along the line of sight over the redshift range z = 2.78-3.28. Its interpretation was facilitated by modeling based on Keck HIRES spectra of the H I Lyα forest (provided by A. Songaila and by M. Rauch and W. Sargent). We find that near the quasar, He II Lyα absorption is produced by discrete clouds, with no significant diffuse gas, this is attributed to a He II "proximity effect" in which the quasar fully ionizes He in the diffuse intergalactic medium, but not the He in denser clouds. By two different methods we calculate that the average He II Lyα opacity at z ≈ 3.15 is τ ≥ 4.8. In the Dobrzycki-Bechtold void in the H I Lyα forest near z = 3.18, the average He II opacity τ = 4.47~+0.48_-0.33. Such large opacities require the presence of a diffuse gas component as well as a soft UV background spectrum, whose softness parameter, defined as the ratio of the photoionization rate in H I over the one in He II S ≡ Γ~J_HI/Γ~J_He II ≈800, indicating a significant stellar contribution. At z = 3.05, there is a distinct region of high He II Lyα transmission that most likely arises in a region where helium is doubly ionized by a discrete local source, quite possibly an AGN. At redshifts z < 2.87, the He II Lyα opacity detected by STIS, τ = 1.88, is significantly lower than at z > 3. Such a reduction in opacity is consistent with Songaila's report that the hardness of the UV background spectrum increases rapidly from z = 3 to z = 2.9.
机译：在哈勃太空望远镜上用太空望远镜成像光谱仪在1.8 A分辨率下观察到了遥远的类星体Q0302--003（z = 3.286）的紫外光谱（1145--1720 A）。获得的总积分时间为23,280 s。光谱清楚地描绘了由He IILyα产生的Gunn-Peterson He II吸收槽，其沿红移范围z = 2.78-3.28的视线。通过基于H ILyα森林的Keck HIRES光谱进行建模（由A. Songaila和M. Rauch和W. Sargent提供），可以促进其解释。我们发现在类星体附近，He IILyα的吸收是由离散的云产生的，没有明显的扩散气体，这归因于He II的“邻近效应”，在类星体中，类星体将He完全电离，但不是他在密云中。通过两种不同的方法，我们计算出在z≈3.15时平均He IILyα不透明度为τ≥4.8。在z = 3.18附近的H Lyya森林中的Dobrzycki-Bechtold空隙中，平均He II不透明度τ= 4.47〜+ 0.48_-0.33。如此大的不透明度需要存在扩散气体成分以及柔和的UV背景光谱，其柔度参数定义为HI中的光电离速率与He II中的光电离率之比S≡Γ〜J_HI /Γ〜J_He II ≈800，表明了巨大的恒星贡献。在z = 3.05时，有一个明显的高He IILyα传输区域，最有可能出现在一个氦被离散的局部来源（很可能是AGN）双重电离的区域中。在红移z <2.87处，STIS检测到的He IILyα不透明性τ= 1.88，远低于在z> 3时。这种不透明性的降低与Songaila的报告一致，即UV背景光谱的硬度从z迅速增加。 = 3至z = 2.9。

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