Title: The Structure and Dynamical Evolution of the Stellar Disk of a Simulated Milky Way-Mass Galaxy Show Chinese title

Title: 一个类似银河系质量星系的恒星盘结构与动力学演化

Abstract: We study the structure, age and metallicity gradients, and dynamical evolution using a cosmological zoom-in simulation of a Milky Way-mass galaxy from the Feedback in Realistic Environments project. In the simulation, stars older than 6 Gyr were formed in a chaotic, bursty mode and have the largest vertical scale heights (1.5-2.5 kpc) by z=0, while stars younger than 6 Gyr were formed in a relatively calm, stable disk. The vertical scale height increases with stellar age at all radii, because (1) stars that formed earlier were thicker "at birth", and (2) stars were kinematically heated to an even thicker distribution after formation. Stars of the same age are thicker in the outer disk than in the inner disk (flaring). These lead to positive vertical age gradients and negative radial age gradients. The radial metallicity gradient is neg- ative at the mid-plane, flattens at larger disk height |Z|, and turns positive above |Z|~1.5kpc. The vertical metallicity gradient is negative at all radii, but is steeper at smaller radii. These trends broadly agree with observations in the Milky Way and can be naturally understood from the age gradients. The vertical stellar density profile can be well-described by two components, with scale heights 200-500 pc and 1-1.5 kpc, respectively. The thick component is a mix of stars older than 4 Gyr which formed through a combination of several mechanisms. Our results also demonstrate that it is possible to form a thin disk in cosmological simulations even with strong stellar feedback. Show Chinese abstract

Abstract: 我们利用来自“真实环境中的反馈”项目的银河系质量星系宇宙学放大模拟，研究了结构、年龄和金属丰度梯度以及动力学演化。在该模拟中，超过6 Gyr的老年恒星以一种混乱的爆发模式形成，并且到z=0时具有最大的垂直尺度高度（1.5-2.5千秒差距），而小于6 Gyr的年轻恒星则以相对平静稳定的盘状模式形成。恒星的垂直尺度高度随所有半径处的恒星年龄增加，因为（1）早期形成的恒星在“出生时”更厚，以及（2）恒星在形成后被动力学加热至更厚的分布。相同年龄的恒星在外盘比内盘更厚（膨胀）。这些导致了正的垂直年龄梯度和负的径向年龄梯度。中平面处的径向金属丰度梯度为负，在更大的盘高|Z|处变平，并在|Z|~1.5千秒差距以上变为正。在所有半径处垂直金属丰度梯度均为负，但在较小半径处更陡峭。这些趋势大致符合银河系的观测结果，并可以从年龄梯度自然理解。垂直恒星密度剖面可以用两个分量很好地描述，其比例高度分别为200-500秒差距和1-1.5千秒差距。厚分量是由超过4 Gyr的老年恒星混合而成，这些恒星通过几种机制的组合形成。我们的结果还表明，即使有强烈的恒星反馈，在宇宙学模拟中仍然可以形成薄盘。