什么样的星系质量会扰动局部的宇宙膨胀？
What galaxy masses perturb the local cosmic expansion?
摘要：
我们使用12个宇宙学$N$ -体模拟的本地集团系统（使徒模型）检查维里质量的主要晕（$M_{\rm vir,1}$和$M_{\rm vir,2}$），质量来自相对运动的晕对（$M_{\rm tim}$），和推断的本地哈勃流（$M_{\rm lhf}$）之间的关系。我们表明，在球形塌陷模型（SCM），三个质量估计之间的对应关系是准确的，即$M_{\rm lhf}=M_{\rm tim}=M_{\rm vir,1}+M_{\rm vir,2}$。然而，与Apostle模拟的比较表明，与SCM所述相反，扰动局部哈勃流并驱动主星系相对轨迹的质量的相对较大部分不包含在$R_{\rm vir}$中，并且“维里外”质量的量在吸积速率较慢的星系中倾向于增加。相比之下，对本星系群周围的奇特速度进行建模，可以对主星系对的维里质量比进行无偏约束。采用在$N$ -天体模拟中发现的外晕轮廓，其尺度为$R\gtrsim R_{\rm vir}$的$ρ\sim R^{-4}$，表明扰动局部哈勃流的星系质量大致对应于单个晕的渐近收敛（总）质量。我们发现，估计$M_{\rm vir}$的基础上的动力学示踪剂在$R\gg R_{\rm vir}$需要先验信息的内部物质分布和增长率的主要星系，这两者通常是难以量化的。
英文摘要：
We use 12 cosmological $N$-body simulations of Local Group systems (the Apostle models) to inspect the relation between the virial mass of the main haloes ($M_{\rm vir,1}$ and $M_{\rm vir,2}$), the mass derived from the relative motion of the halo pair ($M_{\rm tim}$), and that inferred from the local Hubble flow ($M_{\rm lhf}$). We show that within the Spherical Collapse Model (SCM), the correspondence between the three mass estimates is exact, i.e. $M_{\rm lhf}=M_{\rm tim}=M_{\rm vir,1}+M_{\rm vir,2}$. However, comparison with Apostle simulations reveals that, contrary to what the SCM states, a relatively large fraction of the mass that perturbs the local Hubble flow and drives the relative trajectory of the main galaxies is not contained within $R_{\rm vir}$, and that the amount of "extra-virial" mass tends to increase in galaxies with a slow accretion rate. In contrast, modelling the peculiar velocities around the Local Group returns an unbiased constraint on the virial mass ratio of the main galaxy pair. Adopting the outer halo profile found in $N$-body simulations, which scales as $ρ\sim R^{-4}$ at $R\gtrsim R_{\rm vir}$, indicates that the galaxy masses perturbing the local Hubble flow roughly correspond to the asymptotically-convergent (total) masses of the individual haloes. We show that estimates of $M_{\rm vir}$ based on the dynamics of tracers at $R\gg R_{\rm vir}$ require a priori information on the internal matter distribution and the growth rate of the main galaxies, both of which are typically difficult to quantify.
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