了解未知数：星系动力学质量简单估算的不确定性
Knowing the unknowns: uncertainties in simple estimators of galactic dynamical masses
摘要：
观测到的色散支撑星系的恒星运动学常被用来测量动力学质量。最近，恒星的视线速度色散，投影（2D）或去投影（3D）的半光半径，和封闭在半光半径内的总质量之间的几个分析关系，依赖于球面Jeans方程，已被提出。在这里，我们利用APOSTLE宇宙学流体动力学模拟的本地组，以测试的有效性和准确性，这样的质量估计的色散和旋转支持的星系，场和卫星星系，以及不同的质量，形状和速度色散各向异性的星系。我们发现，质量估计的沃克等人。和沃尔夫等人。能够恢复的质量分散为主的系统几乎没有系统偏差，但1-西格玛分散的25%和23%，分别。估计质量的误差主要是由恒星质量分布的3D形状的影响，这是很难约束观测。这种内在的散射成为不确定性的主要来源，估计像银河系的矮椭球（dSph）卫星星系的质量，在它们的大小和速度分散的观测误差很小。这种散射也可能影响来自多个恒星星族的dSphs的内部密度斜率，放松Navarro-Frenk-White轮廓可能被排除在外的重要性，这取决于不同恒星星族的相关属性的相关程度。最后，我们推导出一个新的最佳质量估计，消除了残余偏差，并实现了统计上显着减少的分散到20%的整体分散为主的星系，允许更精确和准确的质量估计。
英文摘要：
The observed stellar kinematics of dispersion-supported galaxies are often used to measure dynamical masses. Recently, several analytical relationships between the stellar line-of-sight velocity dispersion, the projected (2D) or deprojected (3D) half-light radius, and the total mass enclosed within the half-light radius, relying on the spherical Jeans equation, have been proposed. Here, we make use of the APOSTLE cosmological hydrodynamical simulations of the Local Group to test the validity and accuracy of such mass estimators for both dispersion and rotation-supported galaxies, for field and satellite galaxies, and for galaxies of varying masses, shapes, and velocity dispersion anisotropies. We find that the mass estimators of Walker et al. and Wolf et al. are able to recover the masses of dispersion-dominated systems with little systematic bias, but with a 1-sigma scatter of 25 and 23 percent, respectively. The error on the estimated mass is dominated by the impact of the 3D shape of the stellar mass distribution, which is difficult to constrain observationally. This intrinsic scatter becomes the dominant source of uncertainty in the masses estimated for galaxies like the dwarf spheroidal (dSph) satellites of the Milky Way, where the observational errors in their sizes and velocity dispersions are small. Such scatter may also affect the inner density slopes of dSphs derived from multiple stellar populations, relaxing the significance with which Navarro-Frenk-White profiles may be excluded, depending on the degree to which the relevant properties of the different stellar populations are correlated. Finally, we derive a new optimal mass estimator that removes the residual biases and achieves a statistically significant reduction in the scatter to 20 percent overall for dispersion-dominated galaxies, allowing more precise and accurate mass estimates.
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