盖亚惯性参考系和Milky Way盘的倾斜
The Gaia inertial reference frame and the tilting of the Milky Way disk
摘要：
虽然银河系盘和暗物质晕对称面之间的精确关系仍然有些不确定，但相对于惯性参考系的时变盘取向似乎是可能的。分层结构形成模型预测，暗物质晕是三轴的，并且以~2 rad/哈勃时间（~30 muas/yr）的特征速率翻滚。这些模型还预测了一个随时间变化的气体吸积，这样盘的角动量矢量应该与晕的角动量矢量不一致。这些效应，以及大麦哲伦星云的潮汐效应，将导致盘的角动量矢量相对于类星体参考系的旋转。我们评估的准确性，从盖亚的位置和自行可以被称为一个运动学非旋转系统，并表明，自旋矢量的变换从任何刚性自洽目录框架的类星体定义的准惯性系统应被定义为优于1 μ as/年。盖亚对这个惯性系的测定将揭示盘方向随时间变化的任何特征，改进银河系的潜力和动力学模型，测试引力理论，并为人马座矮星系和麦哲伦云的轨道演化提供新的见解。
英文摘要：
While the precise relationship between the Milky Way disk and the symmetry planes of the dark matter halo remains somewhat uncertain, a time-varying disk orientation with respect to an inertial reference frame seems probable. Hierarchical structure formation models predict that the dark matter halo is triaxial and tumbles with a characteristic rate of ~2 rad/Hubble time (~30 muas/yr). These models also predict a time-dependent accretion of gas, such that the angular momentum vector of the disk should be misaligned with that of the halo. These effects, as well as tidal effects of the LMC, will result in the rotation of the angular momentum vector of the disk population with respect to the quasar reference frame. We assess the accuracy with which the positions and proper motions from Gaia can be referred to a kinematically non-rotating system, and show that the spin vector of the transformation from any rigid self-consistent catalog frame to the quasi-inertial system defined by quasars should be defined to better than 1 muas/yr. Determination of this inertial frame by Gaia will reveal any signature of the disk orientation varying with time, improve models of the potential and dynamics of the Milky Way, test theories of gravity, and provide new insights into the orbital evolution of the Sagittarius dwarf galaxy and the Magellanic Clouds.
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