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arXiv 2007.10990astro-ph.GA
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银盘中恒星的空间和运动学成团

Spatial and Kinematic Clustering of Stars in the Galactic Disk

Harshil Kamdar, Charlie Conroy, Yuan-Sen Ting, Kareem El-Badry

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21 pages, 13 figures. Submitted to ApJ
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摘要：

由于恒星的形成和银河系势的非轴对称性，银河系盘在空间上、运动学上和化学上在许多尺度上都是聚集的。在这项工作中，我们使用$1.7 \times 10^6$恒星的样本计算的空间和运动学两点相关函数在1千秒差距的太阳与6D相空间信息可从\textit{Gaia} DR 2。聚类检测的空间尺度为1-300 pc和速度尺度至少为15公里秒$^{-1}$。结合结构，数据具有幂律指数（$ξ(Δr) \propto Δr^γ$）的$γ\approx-2$在大多数空间尺度，这是符合理论预测。在去除束缚结构之后，数据具有对于$<100$ pc的$γ\approx-1$和对于$>100$ pc的$γ\lesssim -1.5$的幂律指数。我们解释这些结果的帮助下，一个新的恒星模拟银河系中的恒星出生在集群轨道在一个现实的潜力，包括旋臂，酒吧，和GMC。我们发现，模拟在很大程度上同意与观察（在2-3倍）在所有的空间和运动尺度。详细地，模拟中的相关函数比在$< 20$ pc尺度下的数据浅，并且比在$> 30$ pc尺度下的数据陡。我们还发现了一个持久的聚类信号中的运动学相关函数的数据在大$Δv$（$>5$公里的$^{-1}$）不存在于模拟。我们推测，观测和模拟之间的这种不匹配可能是由于两个过程不包括在模拟中：分层恒星形成和瞬态旋臂。我们还使用模拟来预测作为成对金属丰度和年龄分离的函数的聚类信号。为了增强聚类信号，需要以$50\%$和$0.05$ dex的精度测量年龄和金属丰度。

英文摘要：

The Galactic disk is expected to be spatially, kinematically, and chemically clustered on many scales due to both star formation and non-axisymmetries in the Galactic potential. In this work we calculate the spatial and kinematic two-point correlation functions using a sample of $1.7 \times 10^6$ stars within 1 kpc of the Sun with 6D phase space information available from \textit{Gaia} DR2. Clustering is detected on spatial scales of 1-300 pc and velocity scales of at least 15 km s$^{-1}$. With bound structures included, the data have a power-law index ($ξ(Δr) \propto Δr^γ$) of $γ\approx-2$ at most spatial scales, which is in line with theoretical predictions. After removing bound structures, the data have a power-law index of $γ\approx-1$ for $<100$ pc and $γ\lesssim -1.5$ for $>100$ pc. We interpret these results with the aid of a novel star-by-star simulation of the Galaxy in which stars are born in clusters orbiting in a realistic potential that includes spiral arms, a bar, and GMCs. We find that the simulation largely agrees with the observations (within a factor of 2-3) at all spatial and kinematic scales. In detail, the correlation function in the simulation is shallower than the data at $< 20$ pc scales, and steeper than the data at $> 30$ pc scales. We also find a persistent clustering signal in the kinematic correlation function for the data at large $Δv$ ($>5$ km s$^{-1}$) not present in the simulations. We speculate that this mismatch between observations and simulations may be due to two processes not included in the simulation: hierarchical star formation and transient spiral arms. We also use the simulations to predict the clustering signal as a function of pair-wise metallicity and age separations. Ages and metallicities measured with a precision of $50\%$ and $0.05$ dex are required in order to enhance the clustering signal.

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