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财团在阿蒙森-斯科特南极站设计和使用一台8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。这项调查将使我们能够研究完整的星系团丰度及其红移演化，并将给出精确的宇宙学约束，这些约束完全独立于超新星距离和宇宙微波背景各向异性测量。样本大小和红移深度将非常适合于利用星系团丰度演化来确定宇宙暗能量分量的状态方程。宇宙学最重要的发现之一是，宇宙中似乎有很大一部分质量(如果不是大部分质量)不是由我们从天文图像中所熟悉的恒星和发光气体组成的，而是由我们从天文图像中所熟悉的暗物质组成的。这种暗物质很少或根本不发出光或其他电磁辐射，到目前为止，人们只知道它的存在是通过它对发光物质施加的引力。有一些迹象表明，暗物质实际上可能甚至不是重子物质。宇宙学家和物理学家非常感兴趣的是，质量的多少部分是以非相互作用的非重子粒子的形式存在的。测量以重子为单位的质量以及宇宙中一个可以被视为“公平样本”的区域的总质量，将提供一个至关重要的直接确定暗物质含量的方法。近年来，正是以大质量星系团的名义发现了这样一个试验台。这些星系团含有大量气体(重子)，这些气体在数百万度的温度下处于高度电离的气体大气中，发出X射线。星系团中几乎所有的重子都被认为处于热相，因此我们很可能是在真正测量星系团中的重子质量。除了发射X射线外，热星系团气体还散射宇宙微波背景(CMB)辐射。这种散射被称为Sunyaev-Zeldovich效应(SZE)，可以用射电望远镜测量。CMB的黑体温度为2.7K，峰值波长约为1 mm。厘米波长的观测将SZE视为光谱的扭曲，即当光子向更高能级散射时，朝向星系团的亮度降低。观测到的衰减量与穿过星系团的视线上的积分电子密度成正比。Sunyaev-Zeldovich效应对于宇宙学和CMB的研究是重要的，主要有两个原因。1)由动力学效应产生的观测“热点”将扭曲CMB各向异性的功率谱。这些都需要从主要的各向异性中分离出来，以便探索膨胀的性质。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.