We analyse a set of cosmological magneto-hydrodynamic simulations of the formation of Milky Way-mass galaxies identified to have a prominent radially anisotropic stellar halo component similar to the so-called “Gaia Sausage” found in the Gaia data. We examine the effects of the progenitor of the Sausage (the Gaia-Enceladus-Sausage, GES) on the formation of major galactic components analogous to the Galactic thick disc and inner stellar halo. We find that the GES merger is likely to have been gas-rich and contribute 10-50% of gas to a merger-induced centrally concentrated starburst that results in the rapid formation of a compact, rotationally supported thick disc that occupies the typical chemical thick disc region of chemical abundance space. We find evidence that gas-rich mergers heated the proto-disc of the Galaxy, scattering stars onto less-circular orbits such that their rotation velocity and metallicity positively correlate, thus contributing an additional component that connects the Galactic thick disc to the inner stellar halo. We demonstrate that the level of kinematic heating of the proto-galaxy correlates with the kinematic state of the population before the merger, the progenitor mass and orbital eccentricity of the merger. Furthermore, we show that the mass and time of the merger can be accurately inferred from local stars on counter-rotating orbits.

中文翻译：

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来自富含气体的盖亚-土卫二香肠合并的银河厚盘和晕的双重起源

我们分析了一组银河系质量星系形成的宇宙磁流体动力学模拟，这些星系被确定具有突出的径向各向异性恒星晕成分，类似于在盖亚数据中发现的所谓的“盖亚香肠”。我们研究了香肠的祖先（盖亚-土卫二-香肠，GES）对类似于银河厚盘和内部恒星晕的主要银河成分形成的影响。我们发现，GES 并合很可能富含气体，并为并合引起的中心集中星暴贡献了 10-50% 的气体，导致快速形成致密的、旋转支撑的厚盘，占据典型的化学厚度。化学丰度空间的圆盘区域。我们发现了富含气体的合并加热了银河系原盘的证据，将恒星散射到不那么圆的轨道上，使得它们的旋转速度和金属丰度呈正相关，从而贡献了一个额外的成分，将银河厚盘连接到内部恒星晕。我们证明了原星系的运动加热水平与合并前种群的运动状态、合并的前身质量和轨道偏心率相关。此外，我们表明可以从反向旋转轨道上的本地恒星准确推断合并的质量和时间。我们证明了原星系的运动加热水平与合并前种群的运动状态、合并的前身质量和轨道偏心率相关。此外，我们表明可以从反向旋转轨道上的本地恒星准确推断合并的质量和时间。我们证明了原星系的运动加热水平与合并前种群的运动状态、合并的前身质量和轨道偏心率相关。此外，我们表明可以从反向旋转轨道上的本地恒星准确推断合并的质量和时间。