Peculiar velocity surveys have non-uniform spatial distributions of tracers, so that the bulk flow estimated from them does not correspond to that of a simple volume such as a sphere. Thus bulk flow estimates are generally not strictly comparable between surveys, even those whose effective depths are similar. In addition, the sparseness of typical surveys can lead to aliasing of small scale power into what is meant to be a probe of the largest scales. Here we introduce a new method of calculating bulk flow moments where velocities are weighted to give an optimal estimate of the bulk flow of an idealized survey, with the variance of the difference between the estimate and the actual flow being minimized. These "minimum variance" estimates can be designed to estimate the bulk flow on a particular scale with minimal sensitivity to small scale power, and are comparable between surveys. We compile all major peculiar velocity surveys and apply this new method to them. We find that most surveys we studied are highly consistent with each other. Taken together the data suggest that the bulk flow within a Gaussian window of radius 50 Mpc/h is 407 km/s toward l=287 and b=8. The large-scale bulk motion is consistent with predictions from the local density field. This indicates that there are significant density fluctuations on very large scales. A flow of this amplitude on such a large scale is not expected in the WMAP5-normalized LCDM cosmology, for which the predicted one-dimensional r.m.s. velocity is ~110 km/s. The large amplitude of the observed bulk flow favors the upper values of the WMAP5 error-ellipse, but even the point at the top of the WMAP5 95% confidence ellipse predicts a bulk flow which is too low compared to that observed at >98% confidence level.
We have performed a large set of high-resolution cosmological simulations using smoothed particle hydrodynamics to study the formation of the first luminous objects in the LCDM cosmology. We follow the collapse of primordial gas clouds in eight early structures and document the scatter in the properties of the first star-forming clouds. Our first objects span formation redshifts from z~10 to z~50 and cover an order of magnitude in halo mas. We find that the physical properties of the central star-forming clouds are very similar in all of the simulated objects despite significant differences in…
我们通过精确测量重子声学振荡（BAO）来优化未来光谱红移测量的设计，特别强调宽场多目标光谱仪（WFMOS）的设计。我们开发了一个模型，预测可能的目标星系的曝光时间和红移的函数的数量密度。我们使用这个数计数模型与拟合公式的准确性BAO测量，以确定不同的调查和仪器设计的有效性。我们搜索通过可用的调查参数空间，以找到最佳的调查方面的暗能量状态方程参数根据暗能量工作组图的优点，包括预测未来的测量从普朗克卫星。我们优化的调查，以测试的LambdaCDM模型，假设星系预先选择使用光度红移有一个恒定的数密度与红移，并使用非线性截止的物质功率谱，随红移的演变。我们发现，线发射星系强烈首选连续发射星系作为目标。最佳测量覆盖红移范围0.8 < z < 1.4，覆盖尽可能宽的区域（6000平方米）。从1500小时观察时间开始）。光谱仪最有效的光纤数量是2，000根，随着额外光纤的增加，测量性能不断提高，直到达到10，000根光纤的平台。在调查参数空间中的最佳点不是高峰值，并没有显着影响，包括即将到来的超新星调查和其他BAO实验的约束。
在加速LCDM宇宙学的遥远未来，大尺度结构的宇宙网由一组处于动态平衡的越来越孤立的晕组成。我们研究的方法，无碰撞的暗物质流体静力学平衡，使用一个大型N体模拟演化到比例因子a = 100，远远超过真空-物质平等时代，aeq ~ 0.75，和53/h Gyr到未来的和谐模型宇宙（Omega_m ~ 0.3，Omega_Lambda ~ 0.7）。晕的径向相空间结构-在a < a_eq处由一对零速度表面包围动态活跃的吸积区域-在a > 10 a_eq处简化，当这些表面合并以创建单个零速度表面时，清楚地定义了晕的外边界rhalo及其封闭的质量mhalo。这个边界接近一个固定的物理尺寸，包含一个平均内部密度约5倍的临界密度，类似于经典的爱因斯坦-德西特模型中的转向值。我们与mhalo目前用于定义晕质量（m200，mvir，m180 b）的其他尺度，并发现m200是总渐近集群质量的一半左右，而m180 b如下的内部零速度表面的演变为< 2 but becomes much larger than the total bound mass for a >3。所有束缚晕物质的径向密度分布都与截断的Hernquist分布很好地拟合。NFW分布提供了与r200的稍微更好的拟合内部，但是在r200 < r < rhalo的范围内太浅了。
