群聚暗能量之球坍縮模型

Abstract

本研究藉由球坍縮模型分析暗能量在星系團結構形成之群聚效應。對於密集區內完全群聚之暗能量，我們將此區塊視為一孤立系統,且系統內物質與暗能量之總能量守恆。在此理論下，我們引入參數 r 代表暗能量的群聚程度，其定義為轉向時暗能量與物質之非線性密度差之比值，因此得以決定球坍縮的過程，以及利用均功原理求得最終穩定態時的非線性密度比 ∆ vir 。同時我們援引近期的觀測數據推算現今之 ∆ vir 並歸納出在 w< −0.9 的暗能量模型下，r 的範圍於 0.5 < r < 0.8 之間為一個標準差(1σ)。另外，我們亦利用線性微擾理論處理早期暗能量擾動的演化，並計算相關物理量，且將兩種分析模式加以比較。儘管此兩種方式所得的結果是一致的，我們所提出的參數化方式卻更加直接簡便，且毋需考慮初始的暗能量擾動及其早期演化。We use the spherical collapse model to investigate the clustering effect of dark energy (DE) in the structure formation of galaxy clusters. For the fully clustered DE, we treat the overdense region as an isolated system and the total energy of matter and DE conserves inside the spherical region. Under this circumstance, we introduce a parameter r to characterize the degree of DE clustering, defined by the nonlinear density contrast ratio of DE to matter at the turnaround epoch, and thus we are able to determine the process of the spherical collapse and obtain the virialized nonlinear overdensity ∆ vir by the virial theorem. The current observational data on galaxy clusters suggests 0.5< r < 0.8 for the clustered DE with w < −0.9 at 1σ level. In addition, we utilize the linear perturbation theory to deal with the evolution of DE perturbation at the early time and calculate the related physical quantities. We compare the two methods and find both results consistent with each other while our method introducing a new parameter is simpler and more straightforward without considering the initial DE perturbation and its evolution at the early time.