The Velocity Distribution Function of Galaxy Clusters as a Cosmological Probe
M. Ntampaka11affiliation: McWilliams Center for Cosmology, Department of Physics, Carnegie Mellon University, Pittsburgh, PA 15213 , H. Trac11affiliation: McWilliams Center for Cosmology, Department of Physics, Carnegie Mellon University, Pittsburgh, PA 15213 , J. Cisewski22affiliation: Department of Statistics, Yale University, New Haven, CT 06520 , and L.C. Price11affiliation: McWilliams Center for Cosmology, Department of Physics, Carnegie Mellon University, Pittsburgh, PA 15213
Abstract
We present a new approach for quantifying the abundance of galaxy clusters and constraining cosmological parameters using dynamical measurements. In the standard method, galaxy line-of-sight velocities, $v$ , or velocity dispersions are used to infer cluster masses, $M$ , to quantify the halo mass function (HMF), $dn(M)/d\log(M)$ , which is strongly affected by mass measurement errors. In our new method, the probability distribution of velocities for each cluster in the sample are summed to create a new statistic called the velocity distribution function (VDF), $dn(v)/dv$ . The VDF can be measured more directly and precisely than the HMF and can be robustly predicted with cosmological simulations which capture the dynamics of subhalos or galaxies. We apply these two methods to realistic (ideal) mock cluster catalogs with (without) interlopers and forecast the bias and constraints on the matter density parameter $\Omega_{m}$ and the amplitude of matter fluctuations $\sigma_{8}$ in flat $\Lambda$ CDM cosmologies. For an example observation of 200 massive clusters, the VDF with (without) interloping galaxies constrains the parameter combination $\smash{\sigma_{8}\,\Omega_{m}^{0.29\ (0
中文速览
用星系团的星系运动速度来推断宇宙学参数，传统做法是先把视线方向速度弥散度转换成团的质量，再去拟合晕质量函数（HMF），但这个质量转换步骤会引入测量误差，并通过"爱丁顿偏差"把对物质密度参数 Ω_m 和物质波动振幅 σ_8 的估计系统性地拉偏。这篇论文提出了一种新统计量——速度分布函数（VDF，velocity distribution function），直接把样本中每个星系团的星系视向速度概率分布叠加起来，绕开质量估计这一环节。作者用多暗物质（MultiDark）N 体模拟制作了理想、中间和含"闯入星系"污染的三套模拟星系团观测目录，分别对 HMF 和 VDF 方法的精度与偏差做了预测，发现对 200 个大质量星系团的观测，VDF 给出的参数组合 σ_8 Ω_m^0.29 约束偏差极小，而含闯入星系的 HMF 则会显著偏向低 Ω_m、高 σ_8。这一结果表明，VDF 是比 HMF 更稳健的宇宙学探针，未来大规模光谱巡天提供更多星系团样本后，将可以大幅提升对宇宙学参数的约束能力。
原文 arXiv:1602.01837;中英对照 + 大白话阅读 https://aha.fim.ai/paper/1602.01837v2