标题： 星系团中的重子分数和速度-温度关系：模型与观测对比 显示英文标题

标题： The Baryon Fraction and Velocity--Temperature Relation in Galaxy Clusters : Models versus Observations

摘要： 对星系团中的观测到的重子分数和速度—温度关系与两个宇宙学模型下的流体动力学模拟进行了比较：标准模型（Ω=1）和低密度平坦模型（Ω=0.45 和\lambda=0.55 ），这两个模型都归一化到COBE背景涨落。 星系团的观测性质包括速度弥散与温度的关系、气体质量与总质量的关系以及气体质量分数与速度弥散的关系。 我们发现，虽然两种宇宙学模型都能很好地再现这些观测函数的形状，但只有低密度CDM模型能够再现观测到的振幅。 星系团的气体质量分数大致反映了模型中的重子分数，且存在轻微的反偏倚。 因此，由于核合成给出的低重子密度，Ω=1 模型在星系团中产生的重子数量比观测到的要少。 按 Ω 缩放我们的结果后，我们发现低密度CDM模型，其中 Ω 大约在 0.3-0.4 之间，最能再现星系团中观测到的平均重子分数。 星系团的观测 β 参数，β = σ²/(kT/μm_p) = 0.94 \pm 0.08，在模型之间区分效果较差；它与低密度CDM模型产生的一致（1.10 \pm 0.22），而略大于 Ω=1 预期值（0.70 \pm 0.14），但仍与之一致。 显示英文摘要

摘要： The observed baryon fraction and velocity--temperature relation in clusters of galaxies are compared with hydrodynamic simulations in two cosmological models : standard (Omega = 1) and a low-density flat (Omega=0.45 and \lambda=0.55) CDM models, normalized to the COBE background fluctuations. The observed properties of clusters include the velocity dispersion versus temperature relation, the gas mass versus total mass relation, and the gas mass fraction versus velocity dispersion relation. We find that, while both cosmological models reproduce well the shape of these observed functions, only low-density CDM can reproduce the observed amplitudes. The cluster gas mass fraction reflects approximately the baryon fraction in the models, with a slight anti-bias. Therefore, due to the low baryon density given by nucleosynthesis, Omega = 1 models produce too few baryons in clusters compared with observations. Scaling our results as a function of Omega, we find that a low-density CDM model, with Omega approximately 0.3 - 0.4, best reproduces the observed mean baryon fraction in clusters. The observed beta parameter of clusters, beta = sigma^2/(k T/mu m_p) = 0.94 \pm 0.08 discriminates less well between the models; it is consistent with that produced by low-density CDM (1.10 \pm 0.22), while it is slightly larger than expected but still consistent with Omega = 1 (0.70 \pm 0.14).