Early Structure Formation and Reionization in a Warm Dark Matter Cosmology
Early Structure Formation and Reionization in a Warm Dark Matter Cosmology
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DOI：
10.1086/376963
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发表时间：
2003-03
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影响因子：
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通讯作者：
N. Yoshida;Aaron Sokasian;L. Hernquist;V. Springel
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文献类型：
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作者：
N. Yoshida;Aaron Sokasian;L. Hernquist;V. Springel
我们使用大宇宙n体/光滑粒子流体动力学模拟研究Λ-dominated宇宙中的第一个结构形成。我们考虑了一个标准的Λ冷暗物质（CDM）模型和一个Λ热暗物质（WDM）模型，其中暗物质粒子的质量取为mX = 10 keV。ΛWDM模型的线性功率谱在波数k = 200 Mpc-1处有一个特征截止，抑制了早期低质量（<106 M☉）非线性天体的形成。由于WDM模型中没有低质量的晕，在高红移时，由氢分子组成的原始气体云的形成效率非常低。在WDM模型中，第一批恒星形成的气体云在z≈21时形成，比CDM模型要晚得多，而且这些气体云的丰度在两种模型之间相差一个数量级。我们通过在气体云中嵌入大质量星族III星来进行辐射传输计算。我们表明，在CDM模型中，电离气体的体积分数在z = 18时上升到接近100%，而在WDM模型中，电离气体的体积分数仍然非常小，只有几个百分点。因此，mX = 10 keV的WDM模型与Wilkinson微波各向异性探测卫星观测到的高光学深度存在强烈的不一致。
We study the first structure formations in Λ-dominated universes using large cosmological N-body/smoothed particle hydrodynamics simulations. We consider a standard Λ cold dark matter (CDM) model and a Λ warm dark matter (WDM) model in which the mass of the dark matter particles is taken to be mX = 10 keV. The linear power spectrum for the ΛWDM model has a characteristic cutoff at a wavenumber k = 200 Mpc-1, suppressing the formation of low-mass (<106 M☉) nonlinear objects early on. The absence of low-mass halos in the WDM model makes the formation of primordial gas clouds with molecular hydrogen very inefficient at high redshifts. The first star-forming gas clouds form at z ≈ 21 in the WDM model, considerably later than in the CDM counterpart, and the abundance of these gas clouds differs by an order of magnitude between the two models. We carry out radiative transfer calculations by embedding massive Population III stars in the gas clouds. We show that the volume fraction of ionized gas rises up close to 100% by z = 18 in the CDM case, whereas that of the WDM model remains extremely small at a level of a few percent. Thus, the WDM model with mX = 10 keV is strongly inconsistent with the high optical depth observed by the Wilkinson Microwave Anisotropy Probe satellite.