arXiv 1909.112502019-09-25astro-ph.GA

星系晕动能对采用的星系势的依赖性

Dependence of Galactic Halo Kinematics on the Adopted Galactic Potential

Young Kwang Kim, Young Sun Lee, Timothy C. Beers

备注：: 21 pages, 16 figures, accepted for publication in ApJ
DOI：: 10.3847/1538-4357/ab3660

摘要：

我们探讨了来自两种常用的银河系势的星系晕运动学性质的差异：St $\ddot{a}$ ckel势和“Galpy”包（MWPotential 2014）中使用的默认类银河系势，利用斯隆数字巡天数据发布12中的可用金属丰度，径向速度和自行的恒星。采用$\ddot{a}$克尔势，我们发现在$Z_{\rm max}$ = 15 kpc和$r_{\rm max}$ = 30 kpc时，金属丰度分布函数的形状和轨道转动分布发生突变（其中$Z_{\rm max}$和$r_{\rm max}$分别是恒星轨道到银河平面和银河中心的最大距离），这表明在这些距离上发生了由内晕恒星星族为主向外晕为主的转变。具有$Z_{\rm max}$ $>$ 15 kpc的恒星表现出$V_{\rm ϕ}$ = $-$ 60 km s $^{-1}$的平均逆行运动，而具有$r_{\rm max}$ $>$ 30 kpc的恒星表现出更大的逆行值，$V_{\rm ϕ}$ = $-$ 150 km s $^{-1}$。这个逆行信号也证实了使用$Gaia$数据发布2获得的径向速度的恒星样本，假设St $\ddot{a}$ ckel势。相比之下，当使用较浅的Galpy势时，仅在$Z_{\rm max}$ = 25 kpc时才发生明显的逆运动变化，并且导出了远不那么极端的逆运动。这种差异的产生是因为在St $\ddot{a}$ CKEL势中具有高度逆行运动的恒星在较浅的Galpy势中是不受约束的，并且具有较低旋转速度的恒星达到较大的$Z_{\rm max}$和$r_{\rm max}$。来自两个潜在的不同的运动学特征表明，所采用的银河系潜在的性质可以强烈影响解释的性质的星系晕。

英文摘要：

We explore differences in Galactic halo kinematic properties derived from two commonly employed Galactic potentials: the St$\ddot{a}$ckel potential and the default Milky Way-like potential used in the "Galpy" package (MWPotential2014), making use of stars with available metallicities, radial velocities, and proper motions from Sloan Digital Sky Survey Data Release 12. Adopting the St$\ddot{a}$ckel potential, we find that the shape of the metallicity distribution function (MDF) and the distribution of orbital rotation abruptly change at $Z_{\rm max}$ = 15 kpc and $r_{\rm max}$ = 30 kpc (where $Z_{\rm max}$ and $r_{\rm max}$ are the maximum distances reached by a stellar orbit from the Galactic plane and from the Galactic center, respectively), indicating that the transition from dominance by the inner-halo stellar population to the outer-halo population occurs at those distances. Stars with $Z_{\rm max}$ $>$ 15 kpc show an average retrograde motion of $V_{\rm ϕ}$ = $-$60 km s$^{-1}$, while stars with $r_{\rm max}$ $>$ 30 kpc exhibit an even larger retrograde value, $V_{\rm ϕ}$ = $-$150 km s$^{-1}$. This retrograde signal is also confirmed using the sample of stars with radial velocities obtained by $Gaia$ Data Release 2, assuming the St$\ddot{a}$ckel potential. In comparison, when using the shallower Galpy potential, a noticeable change in the MDF occurs only at $Z_{\rm max}$ = 25 kpc, and a much less extreme retrograde motion is derived. This difference arises because stars with highly retrograde motions in the St$\ddot{a}$ckel potential are unbound in the shallower Galpy potential, and stars with lower rotation velocities reach larger $Z_{\rm max}$ and $r_{\rm max}$. The different kinematic characteristics derived from the two potentials suggest that the nature of the adopted Galactic potential can strongly influence interpretation of the properties of the Galactic halo.

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