South Pole Observations to Test Cosmological Models

芝加哥大学将领导一个由六个机构组成的联合体，在阿蒙森-斯科特南极站设计和利用一个八米离轴望远镜，以便对星系团进行一次独特而强大的调查，以达到前所未有的红移。这一调查将允许综合集团的丰度和它的红移演化的研究，并将给我们精确的宇宙学约束，这是完全独立的超新星距离和宇宙微波背景各向异性测量。在宇宙学中最重要的发现之一是，宇宙中的大部分（如果不是大多数的话）质量并不是由恒星和发光气体组成的，而这些恒星和发光气体是我们从天文学的天空图像中所熟悉的，而是所谓的暗物质这种暗物质几乎不发射光或其他电磁辐射，到目前为止，只有通过它施加在发光物质上的引力才能知道它的存在。有迹象表明，暗物质实际上甚至可能不是重子物质。对于宇宙学家和物理学家来说，没有相互作用的非重子粒子在质量中所占的比例是一个非常重要的问题。测量宇宙中一个可以被认为是“公平样本”的区域中的重子质量沿着总质量，可以直接确定暗物质的含量。近年来，在大质量星系团的伪装下，已经发现了这样一个试验台。这些星系团包含大量的气体（重子），以高度电离的气体气氛的形式存在，温度高达数百万度，可以发射X射线。星系团中几乎所有的重子都被认为处于热态，因此我们很可能真正测量了星系团中的重子质量。除了发射X射线外，热的星系团气体还散射宇宙微波背景辐射（CMB）。这种散射被称为Sunyaev-Zeldovich效应（SZE），可以使用射电望远镜测量。CMB的黑体温度为2.7 K，辐射光谱峰值波长约为1 mm。厘米波长的观测将SZE视为光谱的扭曲，即当光子向更高的能级散射时，朝向星团的亮度降低。观察到的衰减量与沿着视线方向的积分电子密度成正比。Sunyaev-Zeldovich效应对宇宙学和宇宙微波背景的研究很重要，主要有两个原因。1)由动力学效应产生的观察到的“热点”将使CMB各向异性的功率谱失真。为了探测暴胀的性质，需要将这些各向异性与主要的各向异性分开。2)热SZ效应可以测量，并与X射线观测相结合，以确定宇宙学参数的值，特别是哈勃常数。

The University of Chicago will lead a consortium of six institutions to design and utilize an eight-meter off-axis telescope at Amundsen-Scott South Pole Station in order to carry out a unique and powerful survey of galaxy clusters to unprecedented red shifts. This survey will allow the study of integrated cluster abundance and its red shift evolution, and will give us precise cosmological constraints, which are completely independent of those from supernovae distance and Cosmic Microwave Background anisotropy measurements. The sample size and redshift depth will be ideally suited for using cluster abundance evolution to determine the equation of state of the dark energy component of the universe.One of the most important discoveries in cosmology is that it appears that much, if not most, of the mass in the Universe is made not of stars and glowing gas that is familiar to us from astronomical images of the sky, but of what has been termed dark matter. This dark matter emits little or no light or other electromagnetic radiation, and so far makes its presence known only through the gravitational force it exerts upon the luminous matter. There is some indication that the dark matter may in fact not even be baryonic. Just what fraction of the mass is in the form of non-interacting non-baryonic particles is of great interest to cosmologists and physicists.Measuring the mass in baryons along with the total mass in a region of the Universe that could be considered a "fair sample" would provide a crucial direct determination of the dark matter content. In recent years, just such a test-bed has been found in the guise of massive clusters of galaxies. These clusters contain large amounts of gas (baryons) in the form of a highly ionized atmosphere of gas at temperatures of millions of degrees, which emit X-rays. Nearly all of the baryons in the clusters are believed to be in the hot phase, and so it is likely that we are truly measuring the baryonic mass in the cluster.In addition to emitting X-rays, the hot cluster gas also scatters the cosmic microwave background (CMB) radiation. This scattering, called the Sunyaev-Zeldovich effect (SZE), is measurable using radio telescopes. The CMB has a blackbody temperature of 2.7 K which and a radiation spectrum that peaks at a wavelength of around lmm. Observations at centimeter wavelengths see the SZE as a distortion of the spectrum, i.e. as a reduction in the brightness toward the cluster as the photons are scattered toward a higher energy level. The observed decrement is proportional to the integrated electron density along the line-of-sight through the cluster.The Sunyaev-Zeldovich effect is important to the study of cosmology and the CMB for two main reasons. 1) The observed "hotspots" created by the kinetic effect will distort the power spectrum of CMB anisotropies. These need to be separated from the primary anisotropies in order to probe properties of inflation. 2) The thermal SZ effect can be measured and combined with x-ray observations in order to determine values of cosmological parameters, in particular the Hubble constant.