Ultraviolet background radiation from cosmic structure formation
Ultraviolet background radiation from cosmic structure formation
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DOI：
10.1111/j.1365-2966.2004.07416.x
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发表时间：
2003-09
影响因子：
4.8
通讯作者：
F. Miniati;A. Ferrara;S. White;Simone Bianchi Mpa;G. Sissa;Trieste Cnr;Arcetri
中科院分区：
文献类型：
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作者：
F. Miniati;A. Ferrara;S. White;Simone Bianchi Mpa;G. Sissa;Trieste Cnr;Arcetri
我们计算了宇宙结构形成过程中气体冲击加热产生的热辐射对紫外背景（UVB）的贡献。我们的主要计算是基于Press-Schechter理论的更新版本。这与基于观测到的星系性质和观测到的宇宙星星形成历史的更经验的估计是一致的。热UVB发射的特征在于远超过4赖德的硬光谱。大部分辐射是由质量范围为10 11 - 10 13 M ○的物体产生的。即大星系和小星系团。我们计算了一个复合UVB光谱由于类星体（QSO），恒星和热组件。H和He莱曼极限下的UVB强度之比从z = 2时的60增加到z = 6时的300以上。在高红移下，光致电离率与观测到的冈恩-彼得森效应的比较限制了电离光子从星系中的逃逸分数小于百分之几。在接近1赖德时，热辐射和恒星辐射是相当的，在3、4.5和更高的红移下，分别占总通量的10%、20%和35%。然而，在He II的电离阈值附近，热贡献要强得多。它与类星体的强度已经在红移0.3处相当，并且在红移超过4处占主导地位。热光子本身就足以产生和维持氦II再电离已经在z 6。我们讨论了我们的研究结果的星系际介质的热历史，特别是他II再电离的可能影响。
We calculate the contribution to the ultraviolet background (UVB) from thermal emission from gas shock heated during cosmic structure formation. Our main calculation is based on an updated version of Press-Schechter theory. It is consistent with a more empirical estimate based on the observed properties of galaxies and the observed cosmic star formation history. Thermal UVB emission is characterized by a hard spectrum extending well beyond 4 Ryd. The bulk of the radiation is produced by objects in the mass range 10 11 -10 13 M ○. , i.e. large galaxies and small groups. We compute a composite UVB spectrum due to quasi-stellar object (QSO), stellar and thermal components. The ratio of the UVB intensities at the H and He Lyman limits increases from 60 at z = 2 to more than 300 at z = 6. A comparison of the resulting photoionization rates to the observed Gunn-Peterson effect at high redshifts constrains the escape fraction of ionizing photons from galaxies to be less than a few per cent. Near 1 Ryd, thermal and stellar emission are comparable, amounting to about 10, 20 and 35 per cent of the total flux at redshifts of 3, 4.5 and higher, respectively. However, near the ionization threshold for He II, the thermal contribution is much stronger. It is comparable to the QSO intensity already at redshift ∼3 and dominates at redshifts above 4. Thermal photons alone are enough to produce and sustain He II reionization already at z 6. We discuss the possible implications of our results for the thermal history of the intergalactic medium, in particular for He II reionization.