In studies of the environmental dependence of structure formation, the large scale environment is often thought of as providing an effective background cosmology: e.g. the formation of structure in voids is expected to be just like that in a less dense universe with appropriately modified Hubble and cosmological constants. However, in the excursion set description of structure formation which is commonly used to model this effect, no explicit mention is made of the effective cosmology. Rather, this approach uses the spherical evolution model to compute an effective linear theory growth factor, which is then used to predict the growth and evolution of nonlinear structures. We show that these approaches are, in fact, equivalent: a consequence of Birkhoff's theorem. We speculate that this equivalence will not survive in models where the gravitational force law is modified from an inverse square, potentially making the environmental dependence of clustering a good test of such models.
The abundance of voids and the excursion set formalism
我们提出了一系列的N体模拟的ΛCDM宇宙学的暗物质分布的空洞的数量密度的测量。我们将空洞定义为密度极小值周围ρ v = 0.2ρ m的球形区域，以便将我们的结果与使用偏移集形式主义预测的丰度相关联。利用球形演化模型中δ v =-2.7的线性欠密度，我们发现在从线性到非线性的映射中不守恒数密度的体积守恒模型，在空隙半径1< r（Mpc/h）<15的范围内，与测量的丰度匹配在16%以内。这个模型固定了宇宙在空洞中的体积分数，并假设当相似大小的空洞膨胀1.7倍时，它们会合并，从而达到今天的非线性密度ρ_v = 0.2ρ_m。我们发现Sheth & van de Weygaert（2004）的空洞数密度模型在相同尺度范围内大大高估了丰度。我们发现，体积守恒模型能很好地匹配在较高红移z=0.5和1下模拟测量的空洞数密度，并能正确地预测物质主导的Ω_m = 1宇宙的丰度，误差在25%以内。我们检查了晕分布中的空隙丰度，发现与暗物质相比，较小的空隙（r<10 Mpc/h）较少，而较大的空隙（r>10 Mpc/h）较多。这些结果表明，在晕或星系分布中确定的空洞与暗物质中的潜在空洞分布以复杂的方式相关，如果空洞被用作宇宙学的精确探针，则值得进一步研究。
The concentrations of dark matter haloes provide crucial information about their internal structure and how it depends on mass and redshift -- the so-called concentration-mass-redshift relation, denoted $c(M,z)$. We present here an extensive study of the cosmology-dependence of $c(M,z)$ that is based on a suite of 72 gravity-only, full N-body simulations in which the following cosmological parameters were varied: $σ_{8}$, $Ω_{\mathrm{M}}$, $Ω_{\mathrm{b}}$, $n_{\mathrm{s}}$, $h$, $M_ν$, $w_{0}$ and $w_{\mathrm{a}}$. We characterize the impact of these parameters on concentrations for different…
One of the main predictions of excursion set theory is that the clustering of dark matter haloes only depends on halo mass. However, it has been long established that the clustering of haloes also depends on other properties, including formation time, concentration, and spin; this effect is commonly known as halo assembly bias. We use a suite of gravity-only simulations to study the dependence of halo assembly bias on cosmology; these simulations cover cosmological parameters spanning 10$σ$ around state-of-the-art best-fitting values, including standard extensions of the $Λ$CDM paradigm such a…
