arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 2006.01158astro-ph.SRastro-ph.GA
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Milky Way核球中恒星的年龄分布

The age distribution of stars in the Milky Way bulge

Tawny Sit, Melissa Ness

备注：
Published in ApJ. 17 pages, 23 figures. Updated with minor text revisions and additional citations to match ApJ published version
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摘要：

银河系核球的年龄和化学特征与银河系的形成和演化历史有关。数据驱动的方法和大型调查使恒星年龄和精确的化学丰度能够确定银河系广大地区，包括凸起。在这里，我们使用大炮的数据驱动方法，使用Apache Point Observatory Galaxy Evolution Experiment（APOGEE）DR 14的光谱来推断银河系中125，367颗恒星的年龄和丰度。我们研究了$R_{\text{GAL}}<3.5$ kpc以内的1654颗核球星的年龄和金属丰度。我们专注于领域与$b<12^\circ$，并出到$l<15^\circ$的扩展。我们看到，与太阳附近的恒星（$τ=4$陀螺）相比，球核中的恒星（$τ=8$陀螺）的平均年龄大约是太阳附近恒星（$τ=4$陀螺）的两倍，[Fe/H]的色散更大（$\approx0.38$与0.23 dex相比）。这种年龄梯度主要来自低$α$恒星。沿着银道面看去，核球中心的磁场显示出迄今为止最大的[Fe/H]色散（$σ_{[Fe/H]}\approx0.4$ dex）和视线速度（$σ_{vr}\approx90$ km/s），同时也是年龄色散最小的。沿着经度向外移动，恒星在运动学上变得更冷，在[Fe/H]中分散得更少，但显示出更广泛的年龄范围。我们在$b=8^\circ$纬度处的凸起中看到了X形的特征，但在$b=12^\circ$处没有。未来的APOGEE和其他调查数据，更大的采样，提供了机会，以扩大我们的方法和研究更详细，把更强的约束模型的银河系。

英文摘要：

The age and chemical characteristics of the Galactic bulge link to the formation and evolutionary history of the Galaxy. Data-driven methods and large surveys enable stellar ages and precision chemical abundances to be determined for vast regions of the Milky Way, including the bulge. Here, we use the data-driven approach of The Cannon, to infer the ages and abundances for 125,367 stars in the Milky Way, using spectra from Apache Point Observatory Galaxy Evolution Experiment (APOGEE) DR14. We examine the ages and metallicities of 1654 bulge stars within $R_{\text{GAL}}<3.5$ kpc. We focus on fields with $b<12^\circ$, and out to longitudes of $l<15^\circ$. We see that stars in the bulge are about twice as old ($τ=8$ Gyrs), on average, compared to those in the solar neighborhood ($τ=4$ Gyrs), with a larger dispersion in [Fe/H] ($\approx0.38$ compared to 0.23 dex). This age gradient comes primarily from the low-$α$ stars. Looking along the Galactic plane, the very central field in the bulge shows by far the largest dispersion in [Fe/H] ($σ_{[Fe/H]}\approx0.4$ dex) and line of sight velocity ($σ_{vr}\approx90$ km/s), and simultaneously the smallest dispersion in age. Moving out in longitude, the stars become kinematically colder and less dispersed in [Fe/H], but show a much broader range of ages. We see a signature of the X-shape within the bulge at a latitude of $b=8^\circ$, but not at $b=12^\circ$. Future APOGEE and other survey data, with larger sampling, affords the opportunity to extend our approach and study in more detail, to place stronger constraints on models of the Milky Way.

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