论文标题
宇宙马赫数作为基础暗物质密度场的环境量度
The Cosmic Mach Number as an Environment Measure for the Underlying Dark Matter Density Field
论文作者
论文摘要
我们仅使用宇宙暗物质对$（1.6 $ gpc $/h）^3 $体积进行模拟，我们计算宇宙马赫数（CMN），并对其与密度领域的光环属性和特征的关系进行理论调查，以评估其用途作为环境的方法。 在单个球体上计算的CMN显示与区域的过度密度和密度梯度沿该区域周围的大量流动的相关性。为了减少这些相关性的中位数周围的散布，我们引入了一种新的度量，排序排序的宇宙马赫数（$ \ hat {\ Mathcal {m}} _ g $），该量显示与过度密度$δ= \ frac {ρ-barρ} {\barρ} {\barρ} $。大规模密度梯度的度量以及一个区域中光晕种群的其他平均特性显示与$ \ hat {\ Mathcal {m}} _ g $的紧密相关。我们在第一项实证研究中的结果表明，$ \ hat {\ Mathcal {m}} _ g $是基础密度领域的绝佳代理，因此可以规定区域中数量密度计数的环境。对于$ 10 $至$ 100 mpc $/h的尺度，使用暗物质光环$（> 10^{12} $ m $ _ {\ odot}）$计算的马赫数通常会托管大型星系，这与由于非线性效应的10 \％$ $ $ $ $ $ $ $ $ 10的线性功率频谱的理论预测一致。在RedShifts $ Z \ GEQ 3 $，这些偏差消失了。由于模拟中缺少大规模模式，我们还量化了错误。盒子尺寸$ \ leq 1 $ gpc/$ h $的仿真通常预测CMNS 10-30 \％$ \ sim 100 $ mpc $/h $太小。
Using cosmological dark matter only simulations of a $(1.6$ Gpc$/h)^3$ volume from the Legacy simulation project, we calculate Cosmic Mach Numbers (CMN) and perform a theoretical investigation of their relation with halo properties and features of the density field to gauge their use as an measure of the environment. CMNs calculated on individual spheres show correlations with both the overdensity in a region and the density gradient in the direction of the bulk flow around that region. To reduce the scatter around the median of these correlations, we introduce a new measure, the rank ordered Cosmic Mach number ($\hat{\mathcal{M}}_g$), which shows a tight correlations with the overdensity $δ=\frac{ρ-\barρ}{\barρ}$. Measures of the large scale density gradient as well as other average properties of the halo population in a region show tight correlations with $\hat{\mathcal{M}}_g$ as well. Our results in this first empirical study suggest that $\hat{\mathcal{M}}_g$ is an excellent proxy for the underlying density field and hence environment that can circumvent reliance on number density counts in a region. For scales between $10$ and $100 Mpc$/h, Mach numbers calculated using dark matter halos $(> 10^{12}$ M$_{\odot})$ that would typically host massive galaxies are consistent with theoretical predictions of the linear matter power spectrum at a level of $10\%$ due to non-linear effects of gravity. At redshifts $z\geq 3$, these deviations disappear. We also quantify errors due to missing large scale modes in simulations. Simulations of box size $\leq 1 $ Gpc/$h$ typically predict CMNs 10-30\% too small on scales of$\sim 100$ Mpc$/h$.
