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arXiv 1602.01837astro-ph.CO
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作为宇宙学探测器的星系团速度分布函数

The Velocity Distribution Function of Galaxy Clusters as a Cosmological Probe

M. Ntampaka, H. Trac, J. Cisewski, L. C. Price

摘要:

我们提出了一种新的方法来量化的丰度的星系团和约束宇宙学参数使用动态测量。在标准方法中,星系视线(LOS)速度,$v$,或速度分散被用来推断集群质量,$M$,为了量化晕质量函数(HMF),$dn(M)/d\log(M)$,这是强烈的质量测量误差的影响。在我们的新方法中,对样本中每个聚类的速度概率分布求和,以创建一个称为速度分布函数(VDF)的新统计量$dn(v)/dv$。VDF可以比HMF更直接和精确地测量,并且它也可以通过捕获暗晕或星系动力学的宇宙学模拟来鲁棒地预测。我们将这两种方法应用于模拟星系团星表,预测了平坦$Λ$ CDM宇宙学中物质密度参数$Ω_m$和物质涨落幅度$σ_8$的偏差和约束.对于200个大质量星系团的实例观测,有(无)速度误差的VDF约束了参数组合$σ_8Ω_m^{0.29\ (0.29)} = 0.587 \pm 0.011\ (0.583 \pm 0.011)$,并且仅显示出微小的偏差。然而,在考虑爱丁顿偏差之前,具有动态质量误差的HMF偏向于低$Ω_m$和高$σ_8$,并且基准模型完全超出预测约束。当VDF与来自宇宙微波背景(CMB)的约束相结合时,宇宙学参数之间的简并度可以显著减小。即将到来的光谱调查,探测更大的体积和微弱的幅度将提供更多的集群应用VDF作为宇宙学探测。

英文摘要:

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 (LOS) velocities, $v$, or velocity dispersions are used to infer cluster masses, $M$, in order 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 it can also be robustly predicted with cosmological simulations which capture the dynamics of subhalos or galaxies. We apply these two methods to mock cluster catalogs and forecast the bias and constraints on the matter density parameter $Ω_m$ and the amplitude of matter fluctuations $σ_8$ in flat $Λ$CDM cosmologies. For an example observation of 200 massive clusters, the VDF with (without) velocity errors constrains the parameter combination $σ_8Ω_m^{0.29\ (0.29)} = 0.587 \pm 0.011\ (0.583 \pm 0.011)$ and shows only minor bias. However, the HMF with dynamical mass errors is biased to low $Ω_m$ and high $σ_8$ and the fiducial model lies well outside of the forecast constraints, prior to accounting for Eddington bias. When the VDF is combined with constraints from the cosmic microwave background (CMB), the degeneracy between cosmological parameters can be significantly reduced. Upcoming spectroscopic surveys that probe larger volumes and fainter magnitudes will provide a larger number of clusters for applying the VDF as a cosmological probe.

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