宇宙速度场两点相关的暗晕模型描述

The Halo Model on Velocity Two-point Correlation Function

利用当前宇宙大尺度结构和星系形成领域流行的暗晕模型,对宇宙速度场两点相关函数进行精确的描述。暗晕模型能给出宇宙速度场无论是在线性还是非线性尺度上的估计,而且,模型中考虑了暗晕之间的相对运动,从而解决了在大尺度上模型的预言结果和数值模拟样本统计结果之间不自洽的矛盾。结合暗晕占据数模型,还可以把模型推广到描述星系本动速度两点相关函数上,这无疑给通过星系本动速度来对宇宙大尺度结构和星系形成及演化进行限制方面的研究提供了一个强大的工具,并指出了可能的努力方向。

A number of surveys are expected to directly measure the peculiar velocity of galaxies or clusters. In linear theory, velocities are related to its nearby over density in a simple way, thus, the peculiar velocity is a measurement of density field which can avoid the bias of galaxies with respect to dark matter. There are several ways of extracting useful cosmological information from a velocity survey, among which the two point correlation function of velocity is considered promising. While using the velocity of clusters and dark matter halos as tracers of peculiar velocity field to study the cosmic peculiar velocity correlation function, it is found that the two point correlation function along the line of separation has a negative signal, which can not be explained by the linear theory. Another difficulty remains to be solved is that the velocity is easier to measure on small scale while the measurements on large scale are more probable to be used for constraining theory. We use the halo model to develop the velocity two point correlation function. Even if the velocity of halos is unbiased with that of dark matter, the pair weighted velocity statistics are biased with those of mass due to the fact that the halos are biased with the underlying density field. Associating the pair weighted velocity statistics, we recover the negative velocity correlation along the line of separation on large scales in the halo model frame work. We can also simply extend this model to describe the two point correlation function of galaxies by introducing the halo occupation distribution model. In the near future when the galaxy peculiar velocity survey is available, we can then easily constrain the theory of large scale structure and galaxy formation by comparing the model prediction and directly measurement from observation with this sophisticated model.