天牛数值模拟中的BAO测量、宇宙空洞的统计与成团性分析  

BAO signal detection,statistics and clustering analysis of cosmic voids in Tianniu simulation

作　　者：刘雨 覃健 刘洋 张同杰[1] LIU Yu;QIN Jian;LIU Yang;ZHANG Tongjie(Beijing Normal University,Department of Astronomy,100875,Beijing,China)

机构地区：[1]北京师范大学天文系,北京100875

出　　处：《北京师范大学学报（自然科学版）》2018年第6期716-725,F0003,共11页Journal of Beijing Normal University(Natural Science)

基　　金：国家自然科学基金资助项目(11573006;11528306;10473002);科技部"973"资助项目(2012CB821804)

摘　　要：本文依靠一套空前大规模的N体数值模拟(天牛数值模拟)数据,利用球形过密度方法(spherical overdensity approach)在模拟数据中搜寻并证认暗物质晕,得到了一套高质量的暗物质晕样本数据.通过计算5组数密度不同的大质量暗物质晕(模拟星系)样本的两点相关函数对其BAO信号进行了探测并分析了其成团性.发现更大质量的暗物质晕在更小尺度上成团性更高,并且发现这5条两点相关函数曲线在共动尺度为113.5 h^(-1) Mpc处趋于相交后反转,说明此共动尺度对暗物质晕的大尺度成团性有特殊意义,本文对其应用价值做了详细讨论.利用暗物晕的位置作为示踪体通过Delaunay三角剖分技术将空间剖分成四面体网孔,四面体网孔的外接球被定义为DT(delaunay triangulation)空洞.DT空洞相互交叠并大约为其示踪体数量的7倍并很好地反映出球体所在区域的示踪体空间数密度,这使得可以对此类空洞进行十分有效的成团性分析,这在以往文献定义出的空洞(样本量太少)的成团性分析中是难以做到的.本文对DT空洞做了一些基本的统计研究与基于两点相关函数的成团性分析,发现示踪体数密度的增加使得DT空洞的半径分布整体向小尺度偏移,DT空洞样本的两点相关函数存在一峰值,其对应的尺度与DT空洞样本的平均直径相互对应,并且发现更大半径种类的DT空洞在峰值尺度(DT空洞样本平均直径尺度)的成团性更小.同样也构造出了另一种不交叠的空洞,并且探究了它们的统计性质与成团性质.发现即使示踪体的数密度有所改变,所有不交叠空洞的体积之和总是大约占模拟盒子体积的45%,并对其可能的应用价值进行了讨论.Large-scale N-body simulation data were used in spherical overdensity approach to search and identify dark matter halos in simulation,and to obtain one high quality dark matter halo catalogue.Two-point statistics on top of five magsive halo catalogues (mock galaxy catalogue)were performed with different number densities to detect BAO signals and to investigate clustering properties.Dark matter halos with larger magses were found to cluster higher on smaller scale.The five two-point correlation function curves tended to intersect at the co-moving scale of 113.5h^-1 Mpc,indicating that this co-moving scale had some special significance for halo large-scale clustering.Potential applications in the future were discussed.Halo positions were used to perform partition of the simulation box into tetrahedral meshes using Delaunay triangulation technique. Tetrahedral mesh circumspheres were defined as delaunay triangulation (DT)voids.DT voids overlap each other severely and their radii can well reflect the tracer spatial densities around them.Moreover,their number is approximately 7times of their tracers.This allows us to perform very effective clustering analysis of such voids,not possible for voids defined in previous literature due to low sample size.We performed some basic statistical studies on DT voids and did clustering analyses based on two-point correlation functions.Increase in number density of the tracers was found to makethe radii distribution of the DT voids shift to smaller scale as a whole.A peak in the two-point correlation function of the DT void sample was found,the scale corresponding to average diameter of DT void sample.Construct of disjoint voids was also done,their statistical properties and clustering properties were investigated.Even if the number density of tracers changed,the total volume of all disjoint voids always accounted for approximately 45% of the simulation box volume.Possible applications are discussed.

关 键 词：宇宙学 重子声学振荡 统计方法 宇宙空洞 宇宙大尺度结构 

分 类 号：P159.3[天文地球—天文学]