Formation of Dwarf Galaxies during the Cosmic Reionization
Formation of Dwarf Galaxies during the Cosmic Reionization
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DOI：
10.1086/379784
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发表时间：
2003-09
期刊：
影响因子：
--
通讯作者：
H. Susa;M. Umemura
中科院分区：
文献类型：
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作者：
H. Susa;M. Umemura
本文重新分析了再电离宇宙中紫外背景辐射（UVB）照射下的次银河系天体的光蒸发问题。为此，我们进行三维辐射平滑粒子流体动力学（RSPH）计算，其中的辐射传递是由一个直接的方法解决，包括H2分子的原始气体的非平衡化学也被纳入。注意力集中在UVB的辐射传输效应与Tvir 104 K的亚银河系天体的形成。我们考虑了一个zreion_（17）再电离模型和早期由威尔金森微波各向异性探测器（WMAP）推断的再电离模型（zreion_（17））。我们发现星星的形成受到UVB的明显抑制，但即使在再电离过程中，高密度峰处的重子也会自屏蔽，最终形成一定数量的恒星。从这个意义上说，亚银河系的光蒸发并不像一维球面计算所认为的那样完美。最终的恒星分数取决于坍缩时期和系统的质量，几乎与再电离时期无关。例如，在zreion 107模型中，十分之几的已形成恒星是在宇宙再电离之后诞生的，而在WMAP再电离模型中，超过90%的恒星是在再电离之后诞生的。因此，UVB反馈对冷暗物质（CDM）方案的子结构问题的影响应仔细处理的辐射传输进行评估。形成于高密度峰值的星星团在暗物质势中以无耗散的方式相互结合，从而形成球状系统。因此，这些低质量星系具有大的质光比，例如在本星系群的矮球状星系中观察到的。
We reanalyze the photoevaporation problem of subgalactic objects irradiated by ultraviolet background (UVB) radiation in a reionized universe. For the purpose, we perform three-dimensional radiation smoothed particle hydrodynamics (RSPH) calculations, in which the radiative transfer is solved by a direct method and the nonequilibrium chemistry of primordial gas including H2 molecules is also incorporated. Attention is concentrated on radiative transfer effects on the UVB for the formation of subgalactic objects with Tvir ≲ 104 K. We consider a reionization model with zreion ≈ 7 and also the earlier reionization model (zreion ≈ 17) inferred by the Wilkinson Microwave Anisotropy Probe (WMAP). We find that star formation is suppressed appreciably by UVB, but baryons at high-density peaks are self-shielded even during the reionization, forming some amount of stars eventually. In that sense, the photoevaporation for subgalactic systems is not as perfect as argued by one-dimensional spherical calculations. The final stellar fraction depends on the collapse epoch and the mass of the system, almost regardless of the reionization epoch. For instance, a few tenths of the formed stars are born after the cosmic reionization in the zreion ≈ 7 model, while more than 90% of the stars are born after the reionization in the WMAP reionization model. Thus, the effects of UVB feedback on the substructure problem with a cold dark matter (CDM) scenario should be evaluated with careful treatment of the radiative transfer. The star clusters formed at high-density peaks coalesce with each other in a dissipationless fashion in a dark matter potential, as a resultant forming a spheroidal system. As a result, these low-mass galaxies have large mass-to-light ratios, such as observed in dwarf spheroidal galaxies in the Local Group.