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arXiv 1002.3465astro-ph.COastro-ph.GA
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星系团和星系群密度的演化:高红移时的致密环境

The evolution of the density of galaxy clusters and groups: denser environments at higher redshifts

Bianca M. Poggianti, Gabriella De Lucia, Jesus Varela, Alfonso Aragon-Salamanca, Rose Finn, Vandana Desai, Anja von der Linden, Simon D. M. White

摘要:

我们表明,观测,预计在高z集群的局部密度分布向更高的值相比,在较低的红移集群。为了寻找这种演变的起源,我们分析了从千年模拟中选择的晕样本,并使用半解析模型填充,调查观察到的投影密度和物理3D密度之间的关系,使用从10和3个最近的邻居计算的密度。在观测和模拟中,我们研究了团簇成员数与团簇质量之间的关系,以及每单位团簇质量的成员数。我们发现,所观察到的投影密度的演变反映了转移到更高的值的物理三维密度分布。反过来,这必须与过去每单位星系团体积N/V的星系数量更高有关。我们表明,N/V的演变是由于两种效应的组合:a)遥远的星系团在暗物质(DM)中更密集,这仅仅是因为R_{200}中的DM密度(~星团维里半径)被定义为宇宙临界密度的固定倍数,(b)如果把亮度大于1的星系计算在内,那么每单位星系团DM质量中的星系数与红移和星系团质量都是显著恒定的。被动演化的星等极限我们的研究结果强调,遥远的星系团比今天的星系团密度大得多的环境,无论是在星系的数量和质量,并认为星系在维里化系统的密度条件不依赖于系统的质量。

英文摘要:

We show that, observationally, the projected local density distribution in high-z clusters is shifted towards higher values compared to clusters at lower redshift. To search for the origin of this evolution, we analyze a sample of haloes selected from the Millennium Simulation and populated using semi-analytic models, investigating the relation between observed projected density and physical 3D density, using densities computed from the 10 and 3 closest neighbours. Both observationally and in the simulations, we study the relation between number of cluster members and cluster mass, and number of members per unit of cluster mass. We find that the observed evolution of projected densities reflects a shift to higher values of the physical 3D density distribution. In turn, this must be related with the globally higher number of galaxies per unit of cluster volume N/V in the past. We show that the evolution of N/V is due to a combination of two effects: a) distant clusters were denser in dark matter (DM) simply because the DM density within R_{200} (~the cluster virial radius) is defined to be a fixed multiple of the critical density of the Universe, and b) the number of galaxies per unit of cluster DM mass is remarkably constant both with redshift and cluster mass if counting galaxies brighter than a passively evolving magnitude limit. Our results highlight that distant clusters were much denser environments than today's clusters, both in galaxy number and mass, and that the density conditions felt by galaxies in virialized systems do not depend on the system mass.

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