The Stellar Halo of the Galaxy is Tilted and Doubly Broken
The Stellar Halo of the Galaxy is Tilted and Doubly Broken
复制标题
DOI：
10.3847/1538-3881/ac97e9
复制
发表时间：
2022-08
期刊：
影响因子：
--
通讯作者：
Jiwon Jesse Han;C. Conroy;Benjamin D. Johnson;J. Speagle 沈;A. Bonaca;V. Chandra;R. Naidu;Y. Ting
中科院分区：
文献类型：
--
作者：
Jiwon Jesse Han;C. Conroy;Benjamin D. Johnson;J. Speagle 沈;A. Bonaca;V. Chandra;R. Naidu;Y. Ting
现代的银河系巡天发现了一个古老的合并，它支配着我们银河系的恒星晕（盖亚-香肠-土卫二，GSE）。利用H3巡天的化学丰度和运动学数据，我们从这次合并中识别出了5559颗晕星，它们的径向范围为r Gal = 6- 60 kpc。我们提出了完整的选择功能的H3模型来推断这个吸积组件的恒星晕的密度分布。我们考虑一个一般的椭球主轴允许相对于银河系的中心轴旋转，再加上一个多重破幂律。最适合的模型是一个三轴椭球体（轴比10：8：7），在银河系平面上方向太阳倾斜25°，并且是一个双破幂律，破幂半径为12 kpc和28 kpc。双重破缺幂律解决了长期以来在文献中关于晕破裂半径的二分法，假设是单破缺幂律，那么晕破裂半径要么是150 kpc，要么是150 kpc。N体模拟表明，断裂半径与恒星轨道的远心堆积有关，因此观察到的双断裂为GSE合并的初始条件和演变提供了新的见解。此外，恒星晕的倾斜和三轴性可能意味着一部分底层暗物质晕也是倾斜和三轴的。这对星系的动力学质量建模以及直接暗物质探测实验具有重要意义。
Modern Galactic surveys have revealed an ancient merger that dominates the stellar halo of our galaxy (Gaia–Sausage–Enceladus, GSE). Using chemical abundances and kinematics from the H3 Survey, we identify 5559 halo stars from this merger in the radial range r Gal = 6–60kpc. We forward model the full selection function of H3 to infer the density profile of this accreted component of the stellar halo. We consider a general ellipsoid with principal axes allowed to rotate with respect to the galactocentric axes, coupled with a multiply broken power law. The best-fit model is a triaxial ellipsoid (axes ratios 10:8:7) tilted 25° above the Galactic plane toward the Sun and a doubly broken power law with breaking radii at 12 kpc and 28 kpc. The doubly broken power law resolves a long-standing dichotomy in literature values of the halo breaking radius, being at either ∼15 kpc or ∼30 kpc assuming a singly broken power law. N-body simulations suggest that the breaking radii are connected to apocenter pile-ups of stellar orbits, and so the observed double-break provides new insight into the initial conditions and evolution of the GSE merger. Furthermore, the tilt and triaxiality of the stellar halo could imply that a fraction of the underlying dark matter halo is also tilted and triaxial. This has important implications for dynamical mass modeling of the galaxy as well as direct dark matter detection experiments.