标题： 测量星系团超出其暴发半径的逃逸速度和质量分布 显示英文标题

标题： Measuring the escape velocity and mass profiles of galaxy clusters beyond their virial radius

摘要： 焦散技术仅使用星系的红移来测量星系团的逃逸速度和质量分布，测量范围远超过星系团的视界面，在该范围内动力学平衡不一定成立。我们详细描述了这一技术，并分析了其可能存在的系统误差。 我们将焦散技术应用于从ΛCDM宇宙的大尺度流体动力学模拟中提取出的质量M_200≥10^{14}h^{-1}M_sun的星系团。在星系团内的每平方共动兆秒差距内有几十个红移，平均而言，焦散技术能够以优于10%的精度恢复逃逸速度分布，直至约4倍r_200。 焦散技术还能够在(0.6-4)r_200的范围内以优于10%的精度恢复质量分布，但在较小半径处会高估质量，最高可达70%。这种高估是由于忽略了填充函数F_beta(r)的径向依赖性。当半径从约0.1r_200增加到约4r_200时，单个逃逸速度分布的1σ不确定性从约20%增加到约50%。在半径范围(0.6-4)r_200内，单个质量分布的1σ不确定性介于40%到80%之间。 我们表明，这些不确定性的幅度完全归因于球对称性的假设，这个假设难以放弃。另外，我们可以将该技术应用于通过堆叠单个星系团得到的合成星系团：在这种情况下，逃逸速度分布的1σ不确定性在4倍r_200范围内小于20%。因此，焦散技术提供了可靠的平均分布，可以延伸至其他技术难以或无法探测的区域。 显示英文摘要

摘要： The caustic technique uses galaxy redshifts alone to measure the escape velocity and mass profiles of galaxy clusters to clustrocentric distances well beyond the virial radius, where dynamical equilibrium does not necessarily hold. We provide a detailed description of this technique and analyse its possible systematic errors. We apply the caustic technique to clusters with mass M_200>=10^{14}h^{-1} M_sun extracted from a cosmological hydrodynamic simulation of a LambdaCDM universe. With a few tens of redshifts per squared comoving megaparsec within the cluster, the caustic technique, on average, recovers the profile of the escape velocity from the cluster with better than 10 percent accuracy up to r~4 r_200. The caustic technique also recovers the mass profile with better than 10 percent accuracy in the range (0.6-4) r_200, but it overestimates the mass up to 70 percent at smaller radii. This overestimate is a consequence of neglecting the radial dependence of the filling function F_beta(r). The 1-sigma uncertainty on individual escape velocity profiles increases from ~20 to ~50 percent when the radius increases from r~0.1 r_200 to ~4 r_200. Individual mass profiles have 1-sigma uncertainty between 40 and 80 percent within the radial range (0.6-4) r_200. We show that the amplitude of these uncertainties is completely due to the assumption of spherical symmetry, which is difficult to drop. Alternatively, we can apply the technique to synthetic clusters obtained by stacking individual clusters: in this case, the 1-sigma uncertainty on the escape velocity profile is smaller than 20 percent out to 4 r_200. The caustic technique thus provides reliable average profiles which extend to regions difficult or impossible to probe with other techniques.