STIS Observations of He II Gunn-Peterson Absorption toward Q0302–003
STIS Observations of He II Gunn-Peterson Absorption toward Q0302–003
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STIS 对 Q0302-003 的 He II Gunn-Peterson 吸收的观测
DOI：
10.1086/308719
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发表时间：
1998
期刊：
影响因子：
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通讯作者：
Jonathan N. Winkler
中科院分区：
文献类型：
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作者：
S. Heap;G. Williger;A. Smette;I. Hubeny;M. Sahu;E. Jenkins;T. Tripp;Jonathan N. Winkler
利用哈勃空间望远镜上的空间望远镜成像光谱仪在1.8 μ m分辨率下观测到了遥远类星体Q 0302 -003（z = 3.286）的紫外光谱（1145-1720 μ m）。获得了23，280 s的总积分时间。该光谱清晰地描绘了冈恩-彼得森He II吸收谷，它是由He II Lyα沿着视线在红移范围z = 2.78-3.28产生的。它的解释是通过基于H I Lyα森林的Keck HIRES光谱（由A. Songaila和M. Rauch和W.萨金特）。我们发现，在类星体附近，He II Lyα吸收是由离散的云产生的，没有明显的扩散气体;这是由于He II的“邻近效应”，其中类星体完全电离了弥漫的星系际介质中的He，但在致密的云中没有。用两种不同的方法计算了He Ⅱ Lyα在z = 3.15处的平均不透明度τ ≥ 4.8。在z = 3.18附近的H I Lyα森林中的Dobrzycki-Bechtold空洞中，平均He II不透明度τ = 4.47。如此大的不透明度需要扩散气体成分和软紫外背景光谱的存在，其软度参数定义为H I中的光电离率与He II中的光电离率之比S r/r 800，表明有显著的恒星贡献。在z = 3.05处，有一个明显的高He II Lyα透射区域，很可能出现在一个区域，在该区域，氦被一个离散的本地源（很可能是活动星系核）双重电离。在红移z < 2.87时，STIS探测到的He II Lyα不透明度，τ = 1.88，明显低于z > 3时。这种不透明度的降低与Songaila的报告一致，即UV背景光谱的硬度从z = 3迅速增加到z = 2.9。
The ultraviolet spectrum (1145-1720 Å) of the distant quasar Q0302-003 (z = 3.286) was observed at 1.8 Å resolution with 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. 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/Γ ≃ 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.