TNG100模拟中最具旋转支持的盘状星系的形成
The assembly of the most rotationally supported disc galaxies in the TNG100 simulations
AI总结：
本研究通过TNG100模拟中43个盘主导星系与匹配样本的动力学分解，发现盘星系在较低质量暗晕中形成，并合较少，早期形成盘，且高旋转支持盘与低晕质量和气体角动量对齐相关。
摘要：
盘主导星系在如$\Lambda$CDM这样的层级形成场景中可能难以适应，其中并合是一个重要的增长机制。然而，观测证据表明这些星系很常见。我们试图表征在$\Lambda$CDM框架内导致盘主导星系形成的条件。我们在模拟Illustris TNG100中对恒星质量$M_*=[10^{10} \rm - 10^{11}]\\; \rm M_\odot$的所有星系进行动力学分解。我们选取了一个包含43个大部分为盘状星系的样本，其质量中少于$\sim 10\\%$位于核球成分中。为了比较，我们还研究了另外两个恒星质量匹配的样本：43个中间星系，其质量中约$\sim 30\\%$位于核球中，以及43个具有纯球状形态的星系。我们发现基于恒星动力学的选择能够重现不同形态的预期恒星种群趋势，盘主导星系具有更高的恒星形成率和更年轻的恒星。暗晕自旋似乎对星系形态没有作用。在固定的$M_*$下，我们的大部分盘状和中间样本形成于比球状样本质量低$2$-$10$倍的暗物质晕中，突显了盘星系在保留和凝聚其重子方面具有更高的效率。平均而言，并合在盘星系形成中的普遍性低于球状星系，但存在很大的离散性，包括存在一些大部分为盘状的星系，其恒星中有$15\\%$-$30\\%$来自吸积起源。盘在早期开始形成，早在$9$-$10$ Gyr前就稳定了其较低的垂直速度离散度，尽管盘相对于球状的支配地位是在更近期（$3$-$4$ Gyr前）才确立的。最具旋转支持的盘形成于样本中质量最低且气体角动量分布最对齐的暗晕中。
英文摘要：
Disc dominated galaxies can be difficult to accommodate in a hierarchical formation scenario like $Λ$CDM, where mergers are an important growth mechanism. However, observational evidence indicates that these galaxies are common. We seek to characterise the conditions that lead to the formation of disc dominated galaxies within $Λ$CDM. We use dynamical decomposition in all galaxies with stellar mass $M_*=[10^{10} \rm - 10^{11}]\; \rm M_\odot$ within the simulation Illustris TNG100. We select a sample of 43 mostly-disc galaxies having less than $\sim 10\%$ of their mass into a bulge component. For comparison, we also study two additional stellar-mass matched samples: 43 intermediate galaxies having $\sim 30\%$ of their mass in the bulge and 43 with purely spheroidal-like morphology. We find that the selection based on stellar dynamics is able to reproduce the expected stellar population trends of different morphologies, with higher star-formation rates and younger stars in disc-dominated galaxies. Halo spin seems to play no role in the morphology of the galaxies. At fixed $M_*$, our mostly-disc and intermediate samples form in dark matter haloes that are $2$-$10$ times less massive than the spheroidal sample, highlighting a higher efficiency in disc galaxies to retain and condensate their baryons. On average, mergers are less prevalent in the build up of discs than in spheroidal galaxies, but there is a large scatter, including the existence of mostly-disc galaxies with $15\%$-$30\%$ of their stars from accreted origin. Discs start forming early on, settling their low vertical velocity dispersion as early as $9$-$10$ Gyr ago, although the dominance of the disc over the spheroid gets established more recently ($3$-$4$ Gyr ago). The most rotationally supported discs form in haloes with the lowest mass in the sample and best aligned distribution of angular momentum in the gas.
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