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arXiv 1209.0256astro-ph.GA
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从SEGUE K矮星动力学计算太阳附近的引力势

The Gravitational Potential Near the Sun From SEGUE K-dwarf Kinematics

Lan Zhang, Hans-Walter Rix, Glenn van de Ven, Jo Bovy, Chao Liu, Gang Zhao

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46 pages, 13 figures, 1 table, accepted for publication in The Astrophysical Journal
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摘要：

为了限制太阳附近的银河系引力势（$\sim$ 1.5 kpc），我们推导并模拟了9000个K矮星的空间和速度分布，这些矮星具有SDSS/SEGUE光谱，产生径向速度和丰度（[Fe/H]和[ $α$ /Fe]）。我们首先推导出空间密度分布的恒星的三个丰度选择的子种群占调查的选择功能。各亚种群的垂直分布均呈简单指数分布，垂直扩散曲线近似等温。为了模拟这些数据，我们应用“垂直”的牛仔裤方程，它涉及到可观察到的示踪剂数密度和垂直速度分散的重力势或垂直力。我们探索了一些函数形式的垂直力定律，并同时在同一个潜在的所有丰度选择的子种群的分散和密度分布，并探讨所有参数的协方差使用MCMC。我们的拟合约束盘{ \it质量}尺度高度$\lesssim$ 300 pc和总表面质量密度为$67 \pm 6 M_{\odot} {\rm pc^{-2}}$在$|z| = 1.0$ kpc，其中来自所有恒星的贡献是$42 \pm 5 M_{\odot} {\rm pc^{-2}}$（假设来自$13 M_{\odot} {\rm pc^{-2}}$的冷气体的贡献）。我们发现显着的限制本地暗物质密度的$0.0065\pm0.0023 M_{\odot} {\rm pc^{-3}}$（$0.25\pm0.09 {\rm GeV cm^{-3}} $）。再加上最近的实验，这坚定了$0.0075\pm0.0021 M_{\odot} {\rm pc^{-3}}$（$0.28\pm0.08 {\rm GeV cm^{-3}} $）的最佳估计，与近似圆形的暗物质晕在银河系外围的运动学数据的全球拟合一致。

英文摘要：

To constrain the Galactic gravitational potential near the Sun ($\sim$1.5 kpc), we derive and model the spatial and velocity distribution for a sample of 9000 K-dwarfs that have spectra from SDSS/SEGUE, which yield radial velocities and abundances ([Fe/H] & [$α$/Fe]). We first derive the spatial density distribution for stars of three abundance-selected sub-populations by accounting for the survey's selection function. The vertical profile of these sub-populations are simple exponentials and their vertical dispersion profile is nearly isothermal. To model these data, we apply the `vertical' Jeans Equation, which relates the observable tracer number density and vertical velocity dispersion to the gravitational potential or vertical force. We explore a number of functional forms for the vertical force law, and fit the dispersion and density profiles of all abundance selected sub-populations simultaneously in the same potential, and explore all parameter co-variances using MCMC. Our fits constrain a disk {\it mass} scale height $\lesssim$ 300 pc and the total surface mass density to be $67 \pm 6 M_{\odot} {\rm pc^{-2}}$ at $|z| = 1.0$ kpc of which the contribution from all stars is $42 \pm 5 M_{\odot} {\rm pc^{-2}}$ (presuming a contribution from cold gas of $13 M_{\odot} {\rm pc^{-2}}$). We find significant constraints on the local dark matter density of $0.0065\pm0.0023 M_{\odot} {\rm pc^{-3}}$ ($0.25\pm0.09 {\rm GeV cm^{-3}} $). Together with recent experiments this firms up the best estimate of $0.0075\pm0.0021 M_{\odot} {\rm pc^{-3}}$ ($0.28\pm0.08 {\rm GeV cm^{-3}} $), consistent with global fits of approximately round dark matter halos to kinematic data in the outskirts of the Galaxy.

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