HALO7D. III. Chemical Abundances of Milky Way Halo Stars from Medium-resolution Spectra
HALO7D. III. Chemical Abundances of Milky Way Halo Stars from Medium-resolution Spectra
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DOI：
10.3847/1538-4357/acd33d
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发表时间：
2023-02
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通讯作者：
Kevin A. McKinnon;E. Cunningham;C. Rockosi;P. Guhathakurta;I. Escala;E. Kirby;A. Deason
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作者：
Kevin A. McKinnon;E. Cunningham;C. Rockosi;P. Guhathakurta;I. Escala;E. Kirby;A. Deason
Lambda冷暗物质中的光晕组合：7维观测（HALO7D）调查测量了银河系（MW）恒星光晕中恒星的运动学和化学性质，以了解我们银河系的形成。HALO7D由Keck II/DEIMOS光谱和哈勃太空望远镜组成，测量了四个宇宙组合近红外深河外遗产巡天场中MW晕主序关闭星的固有运动。HALO7D由深铅笔梁组成，使其成为当代其他宽视场调查的补充。我们沿着四个不同的点给出了113颗HALO7D恒星的[Fe/H]和[α/Fe]丰度，在银河系中心的径向范围为~ 10-40 kpc。利用HALO7D的全7D化学动力学数据（三维位置、三维速度和丰度），我们测量了每个场和不同金属量分组子样品的晕速椭球的速度各向异性β。我们发现四个磁场中有两个的恒星在非常径向的轨道上运行，而其余两个的恒星在更各向同性的轨道上运行。在- 2.2和- 1.1指数下，将恒星分别分为高、中、低[Fe/H]仓，我们发现各向异性在仓与仓之间存在差异；有些场在所有仓中都以径向轨道为主，而其他场在[Fe/H]仓之间表现出变化。这些化学动力学上的差异证明了HALO7D磁场与构成MW恒星晕的祖先有着不同的贡献。我们的结果强调了在更小的空间尺度上获得的额外信息，而不是从恒星晕的球面平均值得到的结果。
The Halo Assembly in Lambda Cold Dark Matter: Observations in 7 Dimensions (HALO7D) survey measures the kinematics and chemical properties of stars in the Milky Way (MW) stellar halo to learn about the formation of our Galaxy. HALO7D consists of Keck II/DEIMOS spectroscopy and Hubble Space Telescope–measured proper motions of MW halo main-sequence turnoff stars in the four Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey fields. HALO7D consists of deep pencil beams, making it complementary to other contemporary wide-field surveys. We present the [Fe/H] and [α/Fe] abundances for 113 HALO7D stars in the Galactocentric radial range of ∼10–40 kpc along four separate pointings. Using the full 7D chemodynamical data (3D positions, 3D velocities, and abundances) of HALO7D, we measure the velocity anisotropy, β, of the halo velocity ellipsoid for each field and for different metallicity-binned subsamples. We find that two of the four fields have stars on very radial orbits, while the remaining two have stars on more isotropic orbits. Separating the stars into high-, mid-, and low-[Fe/H] bins at −2.2 and −1.1 dex for each field separately, we find differences in the anisotropies between the fields and between the bins; some fields appear dominated by radial orbits in all bins, while other fields show variation between the [Fe/H] bins. These chemodynamical differences are evidence that the HALO7D fields have different fractional contributions from the progenitors that built up the MW stellar halo. Our results highlight the additional information available on smaller spatial scales compared to results from a spherical average of the stellar halo.