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arXiv 2301.03472astro-ph.GAastro-ph.EPastro-ph.SR
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恒星形成区相空间密度的演化

The evolution of phase space densities in star-forming regions

George A. Blaylock-Squibbs, Richard J. Parker

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13 pages + appendices, 10 figures, accepted for publication in MNRAS
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摘要：

恒星形成区的多维相空间密度（包括位置和速度）可以编码有关恒星和行星形成的初始条件的信息。最近，一个新的度量的基础上的马氏距离已被用来表明，热彗星更有可能被发现周围的系外行星的主恒星在高6D相空间密度，这表明一个更动态的形成环境，为这些行星。然而，后来的研究表明，这一最初的结果可能是由于热彗星的年龄和其宿主恒星的运动学存在偏差。我们测试的Mahalanobis距离和密度的能力，以区分更一般的恒星形成区域与不同的形态，通过将其应用到静态区域，要么是substructured或平滑和集中。我们发现，马氏距离是无法区分不同的形态，和N体模拟的初始条件不能仅使用马氏距离或密度约束。此外，我们发现相空间中的维数越多，马氏密度在区分不同初始条件时的有效性就越小。我们表明，平均三维（x，y，z）Mahalanobis密度和Q参数的区域的组合可以约束其初始维里态。然而，这是由于Q参数的区分能力，而不是来自马哈拉诺比斯密度中印记的任何额外信息。因此，我们建议继续使用多种诊断来确定恒星形成区域的初始条件，而不是依赖于单一的多维度量。

英文摘要：

The multi-dimensional phase space density (both position and velocity) of star-forming regions may encode information on the initial conditions of star and planet formation. Recently, a new metric based on the Mahalanobis distance has been used to show that hot Jupiters are more likely to be found around exoplanet host-stars in high 6D phase space density, suggesting a more dynamic formation environment for these planets. However, later work showed that this initial result may be due to a bias in the age of hot Jupiters and the kinematics of their host stars. We test the ability of the Mahalanobis distance and density to differentiate more generally between star-forming regions with different morphologies by applying it to static regions that are either substructured or smooth and centrally concentrated. We find that the Mahalanobis distance is unable to distinguish between different morphologies, and that the initial conditions of the N-body simulations cannot be constrained using only the Mahalanobis distance or density. Furthermore, we find that the more dimensions in the phase space the less effective the Mahalanobis density is at distinguishing between different initial conditions. We show that a combination of the mean three-dimensional (x, y, z) Mahalanobis density and the Q-parameter for a region can constrain its initial virial state. However this is due to the discriminatory power of the Q-parameter and not from any extra information imprinted in the Mahalanobis density. We therefore recommend continued use of multiple diagnostics for determining the initial conditions of star-forming regions, rather than relying on a single multi-dimensional metric.

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