arXiv 2101.070802021-01astro-ph.GA

盖亚DR2的恒星分布函数和局部垂直势

The Stellar Distribution Function and Local Vertical Potential from Gaia DR2

Haochuan Li, Lawrence M. Widrow

备注：: 15 pages, 16 figures
DOI：: 10.1093/mnras/stab574

摘要：

我们开发了一种新的方法来同时确定垂直的潜力，力和恒星$z-v_z$相空间分布函数（DF）在我们的本地补丁的银河系。我们假设太阳邻域可以被看作是一个一维的动力学平衡系统，并直接将$z-v_z$平面上的数密度拟合到我们所说的有理线性DF（RLDF）模型中。该模型虽然比等温模型多一个参数，但可以看作是一个连续的等温分布函数之和。我们将我们的方法应用于盖亚数据发布2的巨星样本，并表明RLDF提供了一个很好的拟合数据。众所周知的相空间螺旋出现在$z-v_z$平面的残差图中。我们使用最佳拟合的潜力绘制残差的频率和角度的垂直振荡，并显示螺旋映射成一条直线。从它的斜率，我们估计相位螺旋产生的扰动$\sim540$万年前。我们还确定了微分表面密度作为垂直速度色散的函数，也称为。垂直温度分布。这一结果与之前在SDSS/SEGUE G矮星中发现的结果在性质上相似。最后，我们解决参数退化和一维近似的有效性。特别是，从冷子样品，其中的1D近似是更安全的，是更接近文献值比从样品作为一个整体。

英文摘要：

We develop a novel method to simultaneously determine the vertical potential, force and stellar $z-v_z$ phase space distribution function (DF) in our local patch of the Galaxy. We assume that the Solar Neighborhood can be treated as a one-dimensional system in dynamical equilibrium and directly fit the number density in the $z-v_z$ plane to what we call the Rational Linear DF (RLDF) model. This model can be regarded as a continuous sum of isothermal DFs though it has only one more parameter than the isothermal model. We apply our method to a sample of giant stars from Gaia Data Release 2 and show that the RLDF provides an excellent fit to the data. The well-known phase space spiral emerges in the residual map of the $z-v_z$ plane. We use the best-fit potential to plot the residuals in terms of the frequency and angle of vertical oscillations and show that the spiral maps into a straight line. From its slope, we estimate that the phase spirals were generated by a perturbation $\sim540$ Myr years ago. We also determine the differential surface density as a function of vertical velocity dispersion, a.k.a. the vertical temperature distribution. The result is qualitatively similar to what was previously found for SDSS/SEGUE G dwarfs. Finally, we address parameter degeneracies and the validity of the 1D approximation. Particularly, the mid-plane density derived from a cold subsample, where the 1D approximation is more secure, is closer to literature values than that derived from the sample as a whole.

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摘要：

英文摘要：

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