arXiv 2111.096572021-11astro-ph.GAastro-ph.CO

用超高速星探测Milky Way暗物质晕形状的一种新方法

Probing the shape of the Milky Way dark matter halo with hypervelocity stars: a new method

Arianna Gallo, Luisa Ostorero, Sankha Subhra Chakrabarty, Stefano Ebagezio, Antonaldo Diaferio

备注：: 29 pages, 20 figures, 5 tables. Accepted in Astronomy and Astrophysics
发表信息：: A&A 663, A72 (2022)
DOI：: 10.1051/0004-6361/202142679

摘要：

本文提出了一种新的方法，利用超高速恒星样本的银河系质心切向速度来确定银河系暗物质晕引力势的形状。我们计算不同样本的HVS在MW的重子分布是轴对称的和DM潜在的要么是球形的，要么是球状的或三轴的径向依赖轴比的轨迹。我们确定的DM势的形状与分布的纬向速度$|v_{\vartheta}|$在轴对称的银河系的潜力，或与分布的$|v_{\vartheta}|$和一个函数$\bar v_φ$的方位角速度在非轴对称的银河系的潜力。我们通过比较$|v_{\vartheta}|$和$\bar v_φ$的分布与在不同形状的DM晕中行进的HVS的模拟样品的相应分布来恢复DM势的正确形状。我们使用的$\sim 800$ HVSs的最大可能的样品$4~M_\odot$抛出的希尔斯机制的速度$\sim 10^{-4}$年$^{-1}$，目前向外，位于超过10千秒差距从银河系中心。在我们的理想情况下，银河系的速度为零的不确定性和没有观测的限制，我们的方法恢复正确的形状的DM潜在的成功率$S\gtrsim 89\%$在轴对称的银河系的潜力，和$S > 96\%$在探索的非轴对称的情况下。不成功的情况下产生的DM潜力的轴比是由$\pm 0.1$关闭。成功率随着样本量的减少而降低：例如，对于球形DM晕圈，当样本量从$\sim 800$减少到$\sim 40$ HVS时，$S$从$\sim 98\%$减少到$\sim 38\%$。因此，一个强大的DM电位的形状的确定，需要数百个真正的HVS的银河系速度的措施。

英文摘要：

We propose a new method to determine the shape of the gravitational potential of the dark matter (DM) halo of the Milky Way (MW) with the galactocentric tangential velocities of a sample of hypervelocity stars (HVSs). We compute the trajectories of different samples of HVSs in a MW where the baryon distribution is axisymmetric and the DM potential either is spherical or is spheroidal or triaxial with radial-dependent axis ratios. We determine the shape of the DM potential with the distribution of the latitudinal velocity $|v_{\vartheta}|$ in axisymmetric Galactic potentials, or with the distribution of $|v_{\vartheta}|$ and of a function $\bar v_φ$ of the azimuthal velocity in non-axisymmetric Galactic potentials. We recover the correct shape of the DM potential by comparing the distribution of $|v_{\vartheta}|$ and $\bar v_φ$ against the corresponding distributions of mock samples of HVSs that traveled in DM halos of different shapes. We use the largest possible sample of $\sim 800$ HVSs of $4~M_\odot$ ejected with the Hills mechanism at a rate $\sim 10^{-4}$ yr$^{-1}$, currently outgoing, and located at more than 10 kpc from the Galactic center. In our ideal case of galactocentric velocities with null uncertainties and no observational limitations, our method recovers the correct shape of the DM potential with a success rate $S\gtrsim 89\%$ in axisymmetric Galactic potentials, and $S > 96\%$ in the explored non-axisymmetric cases. The unsuccessful cases yield axis ratios of the DM potential that are off by $\pm 0.1$. The success rate decreases with decreasing sample size: for example, for a spherical DM halo, $S$ drops from $\sim 98\%$ to $\sim 38\%$ when the sample size decreases from $\sim 800$ to $\sim 40$ HVSs. A robust determination of the shape of the DM potential thus requires the measure of the galactocentric velocity of a few hundred genuine HVSs.

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英文摘要：

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