是什么导致了盘的形成和暴胀式恒星形成的终结？
What Causes The Formation of Disks and End of Bursty Star Formation?
AI总结：
本研究通过大量数值模拟探究星系从暴胀式恒星形成的椭球形态向平滑恒星形成的盘状形态转变的成因，发现二者均由引力势驱动但机制不同，明确了质量分布集中度和逃逸速度分别对盘形成与恒星形成模式转变的关键作用。
摘要：
星系在成长过程中会从具有“暴胀式”恒星形成历史（SFHs）的不规则/椭球形态，转变为具有平滑恒星形成历史的盘状形态。但即便在模拟研究中，这类转变的直接物理成因仍不明确。为此，我们在大量数值实验中探究了这一问题，这些实验重新运行了物理参数差异极大的部分宇宙学模拟，并通过已有的FIRE（反馈于现实环境）模拟进行了进一步验证。\n我们的研究表明，气体供给、冷却/热力学过程、恒星形成模型、图姆雷（Toomre）尺度、星系动力学时标以及反馈属性，都不是这些转变的直接诱因。相反，盘的形成和暴胀式恒星形成的停止均由引力势驱动，但驱动方式有所不同。当质量分布的形状（相对于圆化半径）变得足够中心集中时，会促进盘的形成：我们证明这会提供一个明确的动力学中心，不再支持在集中度较低的分布中可无限持续且能高效破坏盘的全局“呼吸模式”，促进轨道混合以形成相干角动量，并使盘保持稳定。\n当恒星形成半径处的引力势或逃逸速度（而非圆周速度）变得足够大，使得冷的、大质量负载（动量守恒）的外流被捕获/限制在星系附近，而非在暴胀后逃逸时，平滑的恒星形成就会得到促进。我们讨论了其中的详细物理机制、这些条件在宇宙学背景下如何产生、它们与其他相关现象（例如内暗晕位力化、盘的垂直“沉降”）的关联，以及相关观测结果。
英文摘要：
As they grow, galaxies can transition from irregular/spheroidal with 'bursty' star formation histories (SFHs), to disky with smooth SFHs. But even in simulations, the direct physical cause of such transitions remains unclear. We therefore explore this in a large suite of numerical experiments re-running portions of cosmological simulations with widely varied physics, further validated with existing FIRE simulations. We show that gas supply, cooling/thermodynamics, star formation model, Toomre scale, galaxy dynamical times, and feedback properties do not have a direct causal effect on these transitions. Rather, both the formation of disks and cessation of bursty star formation are driven by the gravitational potential, but in different ways. Disk formation is promoted when the mass profile becomes sufficiently centrally-concentrated in shape (relative to circularization radii): we show that this provides a well-defined dynamical center, ceases to support the global 'breathing modes' which can persist indefinitely in less-concentrated profiles and efficiently destroy disks, promotes orbit mixing to form a coherent angular momentum, and stabilizes the disk. Smooth SF is promoted by the potential or escape velocity (not circular velocity) becoming sufficiently large at the radii of star formation that cool, mass-loaded (momentum-conserving) outflows are trapped/confined near the galaxy, as opposed to escaping after bursts. We discuss the detailed physics, how these conditions arise in cosmological contexts, their relation to other correlated phenomena (e.g. inner halo virialization, vertical disk 'settling'), and observations.
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