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arXiv 2003.01132astro-ph.GA
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银盘中动力学螺旋扰动的强度

The Strength of the Dynamical Spiral Perturbation in the Galactic Disk

Anna-Christina Eilers, David W. Hogg, Hans-Walter Rix, Neige Frankel, Jason A. S. Hunt, Jean-Baptiste Fouvry, Tobias Buck

摘要:

银河系中平面内亮红巨星的平均银心径向速度$\langle v_{R}\rangle(R,φ)$显示出一个螺旋形的特征,它可能反映了银河系盘对引力势非轴对称扰动的响应。我们应用一个简单的稳态玩具模型的对数螺旋线来解释这些意见,并找到一个很好的定性和定量的匹配。假设引力位扰动的振幅与盘的表面质量密度成正比,当选择固定的模式速度$Ω_{\mathrm p}=12\,\rm km\,s^{-1}\,kpc^{-1}$时,我们估计在太阳半径处的表面质量密度振幅为$Σ_{\rm max} (R_{\odot})\approx 5.5\,\rm M_{\odot}\,pc^{-2}$。结合当地的磁盘密度,这意味着一个表面的质量密度之间的臂和臂间的区域约$\pm 10\%$在太阳半径的对比度,随着向更大的半径增加。我们的模型约束的动态螺旋臂的俯仰角近似为$12^{\circ}$。

英文摘要:

The mean Galactocentric radial velocities $\langle v_{R}\rangle(R,φ)$ of luminous red giant stars within the mid-plane of the Milky Way reveal a spiral signature, which could plausibly reflect the response to a non-axisymmetric perturbation of the gravitational potential in the Galactic disk. We apply a simple steady-state toy model of a logarithmic spiral to interpret these observations, and find a good qualitative and quantitative match. Presuming that the amplitude of the gravitational potential perturbation is proportionate to that in the disk's surface mass density, we estimate the surface mass density amplitude to be $Σ_{\rm max} (R_{\odot})\approx 5.5\,\rm M_{\odot}\,pc^{-2}$ at the solar radius when choosing a fixed pattern speed of $Ω_{\mathrm p}=12\,\rm km\,s^{-1}\,kpc^{-1}$. Combined with the local disk density, this implies a surface mass density contrast between the arm and inter-arm regions of approximately $\pm 10\%$ at the solar radius, with an increases towards larger radii. Our model constrains the pitch angle of the dynamical spiral arms to be approximately $12^{\circ}$.

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