向层状磁流体动力学风驱动盘中建立全球模型：采用种群合成方法研究低粘性与吸积层厚度的影响
Towards a global model for planet formation in layered MHD wind-driven discs: A population synthesis approach to investigate the impact of low viscosity and accretion layer thickness
AI总结：
本文通过种群合成方法研究低粘性与吸积层厚度对行星形成的影响，发现薄层导致原地形成，厚层导致迁移热木星，揭示II型迁移模式与盘结构的关联。
摘要：
行星形成本质上与原行星盘演化密切相关，近期发展表明其驱动因素是磁化风而非湍流粘性。我们研究磁流体动力学（MHD）风驱动盘中的行星形成，假设吸积发生在弱湍流中层上方的层状表面层中。我们的目标是评估最近流体动力学结果的全球影响，包括中层加热效率低下以及存在两种II型迁移模式：慢粘性主导和快速风驱动迁移。我们进行了单胚胎行星种群合成，测试了不同初始盘条件（即盘质量、大小和角动量传输）、胚胎起始位置以及不同吸积层厚度$\Sigma_\text{active}$的假设方案。薄（$\lesssim0.01\mathrm{g\,cm^{-2}}$）或快速（$\gtrsim12\%$声速）吸积层导致慢速粘性主导模式，强烈限制II型迁移的范围。对于厚（$\gtrsim1\mathrm{g\,cm^{-2}}$）或慢速（$\lesssim3\%$声速）吸积层，快速风驱动的II型迁移频繁发生，导致远距离向内迁移，一旦行星达到足以阻挡吸积层的质量就会开始。盘限制的气体吸积也受到深且早期间隙开启的强烈影响，限制最大巨行星质量。这些影响强烈影响最终的质量-距离分布。对于薄层，巨行星在进入II型迁移后几乎原地形成，这在几地球质量时就已经发生，而厚层导致许多迁移的热木星。总体而言，我们发现虽然新兴行星种群的全球属性相对于经典粘性盘被强烈修改，但观测到的种群的关键属性可以在这一新范式中重现。
英文摘要：
Planet formation is inherently linked to protoplanetary disc evolution, which recent developments suggest is driven by magnetised winds rather than turbulent viscosity. We study planet formation in magnetohydrodynamic (MHD) wind-driven discs, assuming accretion occurs in a laminar surface layer above a weakly turbulent midplane. Our goal is to assess the global consequences of recent hydrodynamical results, including inefficient midplane heating and the existence of two Type II migration regimes: slow viscosity-dominated and fast wind-driven migration. We perform single-embryo planetary population syntheses with varying initial disc conditions (i.e. disc mass, size and angular momentum transport), and embryo starting locations, testing different prescriptions for the accretion layer thickness $Σ_\text{active}$. Thin ($\lesssim0.01\mathrm{g\,cm^{-2}}$) or fast ($\gtrsim12\%$ sonic velocity) accretion layers result in slow, viscosity-dominated regime which strongly limits the extent of Type II migration. For thick ($\gtrsim1\mathrm{g\,cm^{-2}}$) or slow ($\lesssim3\%$ sonic velocity) accretion layers, fast wind-driven Type II migration occurs frequently, leading to long-range inward migration that sets in once planets reach masses sufficient to block the accreting layer. Disk-limited gas accretion is also strongly affected by deep and early gap opening, limiting maximum giant planet masses. These effects strongly influence the final mass-distance distribution. For thin layers, giant planets form nearly in situ once they have entered Type II migration, which happens already at a few Earth masses, while thick layers lead to numerous migrated Hot Jupiters. Overall, we find that while the global properties of the emerging planet population are strongly modified relative to classical viscous discs, key properties of the observed population can be reproduced within this new paradigm.
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