arXiv 2006.162832020-06astro-ph.GA

用自行选择晕样品测定Milky Way的逃逸速度

Determination of the escape velocity of the Milky Way using a proper motion selected halo sample

Helmer H. Koppelman, Amina Helmi

备注：: 14 pages, 13 figures, accepted for publication in A&A
发表信息：: A&A 649, A136 (2021)
DOI：: 10.1051/0004-6361/202038777

摘要：

{ \it Gaia}任务提供了有史以来最大的具有切向速度信息的源目录。然而，使用这个目录进行动力学研究是困难的，因为大多数恒星缺乏视线速度测量。最近，我们提出了一个选择的$\sim 10^7$晕星的准确距离，已选定的基础上，他们的测光和自行。使用这个例子，我们用幂律分布来模拟速度分布的尾部，这是一种由\cite{Leonard1990THESPEED}首先建立的常用方法。这是有史以来第一次，我们使用切向速度精确测量了前所未有的数量晕星估计逃逸速度。在太阳附近，我们得到了一个非常精确的逃逸速度的估计，它是$497^{+8}_{-8}~{\rm km/s}$。这一估计很可能偏低，我们最好的猜测是10%。因此，真实的逃逸速度很可能更接近于$550~{\rm km/s}$。逃逸速度直接限制了银河系的总质量。为了找到最佳的拟合晕质量和浓度参数，我们调整了现实的银河系潜力的黑暗（球形NFW）晕，同时保持太阳半径固定在$v_c(R_\odot) = 232.8~{\rm km/s}$的圆速度。所得晕圈参数为$M_{200}^{+10\%} = 1.11^{+0.08}_{-0.07} \cdot10^{12} ~{\rm M}_\odot$和浓度参数$c^{+10\%} = 11.8^{+0.3}_{-0.3}$，其中我们使用明确的符号表示这些参数已针对10\%偏倚进行了校正。内星系的逃逸速度随银心距的斜率与基于银河系模型的结果一致。奇怪的是，我们发现一个分歧超出了太阳半径，这可能是一个影响的速度分布的形状变化，并可能与速度块的存在。

英文摘要：

The {\it Gaia} mission has provided the largest catalogue ever of sources with tangential velocity information. However, using this catalogue for dynamical studies is difficult because most of the stars lack line-of-sight velocity measurements. Recently, we presented a selection of $\sim 10^7$ halo stars with accurate distances that have been selected based on their photometry and proper motions. Using this sample, we model the tail of the velocity distribution with a power-law distribution, a commonly used approach first established by \cite{Leonard1990THESPEED}. For the first time ever we use tangential velocities measured accurately for an unprecedented number of halo stars to estimate the escape velocity. In the solar neighbourhood, we obtain a very precise estimate of the escape velocity which is $497^{+8}_{-8}~{\rm km/s}$. This estimate is most likely biased low, our best guess is by 10\%. As a result, the true escape velocity most likely is closer to $550~{\rm km/s}$. The escape velocity directly constrains the total mass of the Milky Way. To find the best fitting halo mass and concentration parameter we adjusted the dark (spherical NFW) halo of a realistic Milky Way potential while keeping the circular velocity at the solar radius fixed at $v_c(R_\odot) = 232.8~{\rm km/s}$. The resulting halo parameters are $M_{200}^{+10\%} = 1.11^{+0.08}_{-0.07} \cdot10^{12} ~{\rm M}_\odot$ and concentration parameter $c^{+10\%} = 11.8^{+0.3}_{-0.3}$, where we use the explicit notation to indicate that these have been corrected for the 10\% bias. The slope of the escape velocity with galactocentric distance is as expected in the inner Galaxy based on Milky Way models. Curiously, we find a disagreement beyond the solar radius which is likely an effect of a change in the shape of the velocity distribution and could be related to the presence of velocity clumps.

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