Born this way: thin disc, thick disc, and isotropic spheroid formation in FIRE-2 Milky Way–mass galaxy simulations
Born this way: thin disc, thick disc, and isotropic spheroid formation in FIRE-2 Milky Way–mass galaxy simulations
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DOI：
10.1093/mnras/stad1806
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发表时间：
2022-10
影响因子：
4.8
通讯作者：
Sijie Yu;J. Bullock;Alex Gurvich;Zachary Hafen;J. Stern;M. Boylan-Kolchin;C. Faucher-Giguère;
中科院分区：
文献类型：
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作者：
Sijie Yu;J. Bullock;Alex Gurvich;Zachary Hafen;J. Stern;M. Boylan-Kolchin;C. Faucher-Giguère;
我们使用FIRE-2 ΛCDM宇宙学放大模拟，通过研究银河系主要祖先中形成的恒星从诞生到现在的轨道演化，来研究银河系质量星系的形成。我们根据原位恒星的轨道圆度将其分为各向同性球体、厚盘和薄盘，并表明这些成分分别是按时间顺序从早到晚组装的。所有模拟的星系都经历了恒星形成的早期阶段，然后过渡到后期的稳定阶段。这种转变与内部CGM的病毒化时间一致。在早期爆发阶段，星系形态不规则，新的恒星在径向轨道上诞生；这些恒星演化成今天的各向同性球体。大部分厚盘恒星形成于中间时期，在团块盘“向上旋转”阶段，略晚于球状恒星形成的高峰期。在后期，一旦CGM开始活跃，恒星形成过程“冷却”下来，恒星就会在一个狭窄平面内的圆形轨道上诞生。如今，这些恒星大多居住在薄圆盘上。一般来说，今天具有盘状或球状轨道的恒星就是这样诞生的。在我们的模拟中，盘的合并和长期过程确实会影响运动学，但在z = 0处填充厚盘和原位球体种群时仅起次要作用。球体、厚盘和薄盘种群的年龄分布与稳态相变时间的尺度自相似，这表明形态年龄定年可以与星系中CGM病毒化时间联系起来。
We investigate the formation of Milky Way–mass galaxies using FIRE-2 ΛCDM cosmological zoom-in simulations by studying the orbital evolution of stars formed in the main progenitor of the galaxy, from birth to the present day. We classify in situ stars as isotropic spheroid, thick-disc, and thin-disc according to their orbital circularities and show that these components are assembled in a time-ordered sequence from early to late times, respectively. All simulated galaxies experience an early phase of bursty star formation that transitions to a late-time steady phase. This transition coincides with the time that the inner CGM virializes. During the early bursty phase, galaxies have irregular morphologies and new stars are born on radial orbits; these stars evolve into an isotropic spheroidal population today. The bulk of thick-disc stars form at intermediate times, during a clumpy-disc ‘spin-up’ phase, slightly later than the peak of spheroid formation. At late times, once the CGM virializes and star formation ‘cools down,’ stars are born on circular orbits within a narrow plane. Those stars mostly inhabit thin discs today. Broadly speaking, stars with disc-like or spheroid-like orbits today were born that way. Mergers on to discs and secular processes do affect kinematics in our simulations, but play only secondary roles in populating thick-disc and in situ spheroid populations at z = 0. The age distributions of spheroid, thick disc, and thin disc populations scale self-similarly with the steady-phase transition time, which suggests that morphological age dating can be linked to the CGM virialization time in galaxies.