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首页> 外文期刊>The Astrophysical journal >AN ANALYTICAL MODEL FOR THE TRIAXIAL COLLAPSE OF COSMOLOGICAL PERTURBATIONS
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AN ANALYTICAL MODEL FOR THE TRIAXIAL COLLAPSE OF COSMOLOGICAL PERTURBATIONS

机译：宇宙扰动三轴倒塌的解析模型

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We present an analytical model for the nonspherical collapse of overdense regions out of a Gaussian random field of initial cosmological perturbations. The collapsing region is treated as an ellipsoid of constant density, acted upon by the quadrupole tidal shear from the surrounding matter. The dynamics of the ellipsoid is set by the ellipsoid self-gravity and the external quadrupole shear. Both forces are linear in the coordinates and therefore maintain homogeneity of the ellipsoid at all times. The amplitude of the external shear is evolved into the nonlinear regime in thin spherical shells that are allowed to move only radially according to the mass interior to them. The full dynamical equations then reduce to a set of nine second-order ordinary differential equations, which reproduce the linear regime behavior but can be evolved past turnaround, well into the nonlinear regime. We describe how the initial conditions can be drawn in the appropriate correlated way from a random field of initial density perturbations. The model is applied to a restricted set of initial conditions that are more suitable to the above approximations; most notably we focus on the properties of rare high-density peaks (approx > 2 σ). By considering many random realizations of the initial conditions, we calculate the distribution of shapes and angular momenta acquired by objects through the coupling of their quadrupole moment to the tidal shear. The average value of the spin parameter, < λ > ≈ 0.04, is found to be only weakly dependent on the system mass, the mean cosmological density, or the initial power spectrum of perturbations, in agreement with N-body simulations. For the cold dark matter power spectrum, most objects evolve from a quasi-spherical initial state to a pancake or filament and then to complete virialization. Low-spin objects tend to be more spherical. The evolution history of shapes is primarily induced by the external shear and not by the initial triaxiality of the objects. The statistical distribution of the triaxial shapes of collapsing regions can be used to test cosmological models against galaxy surveys on large scales.
机译：我们提出了一个高解析随机场的初始宇宙学扰动的高密度区域非球面崩溃的分析模型。塌陷区被视为恒定密度的椭圆体，受到来自周围物质的四极潮汐剪切作用。椭球的动力学由椭球自重和外部四极杆剪切力决定。两种力在坐标上都是线性的，因此始终保持椭圆体的均匀性。外部剪切的振幅在薄的球形壳中演变为非线性状态，该球形壳仅根据其内部质量径向移动。然后，完整的动力学方程式可简化为一组九个二阶常微分方程式，该方程式可再现线性状态的行为，但可以演变为经过周转，然后发展为非线性状态。我们描述了如何从初始密度扰动的随机场中以适当的相关方式得出初始条件。该模型应用于一组受限的初始条件，这些条件更适合于上述近似值；最值得注意的是，我们专注于稀有高密度峰（大约> 2σ）的特性。通过考虑初始条件的许多随机实现，我们通过对象的四极矩与潮汐剪切力的耦合来计算形状和角矩的分布。与N体模拟相一致，发现自旋参数的平均值<λ>≈0.04仅弱依赖于系统质量，平均宇宙学密度或扰动的初始功率谱。对于冷暗物质功率谱，大多数对象从准球形初始状态演变为薄饼或细丝，然后完成玻璃化。低自旋物体往往更球形。形状的演变历史主要是由外部剪切引起的，而不是由对象的初始三轴性引起的。塌陷区域的三轴形状的统计分布可用于针对大规模星系调查测试宇宙学模型。

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