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arXiv 2002.01941astro-ph.GA
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MOND中指数盘星系的形成

The formation of exponential disk galaxies in MOND

Nils Wittenburg, Pavel Kroupa, Benoit Famaey

摘要:

星系的形成和演化在很大程度上取决于恒星和气体的动力学,而恒星和气体的动力学又受引力定律的支配。为了研究Milgromian引力(MOND)中星系的形成和演化,我们采用Phantom of Ramses(POR)程序进行了流体动力学模拟。这是MOND首次对星系形成进行详细的流体动力学模拟,包括恒星形成、恒星反馈、辐射转移和超新星。这些模型从简化的初始条件开始,以早期宇宙中孤立的旋转气体球的形式。这些坍缩形成的晚型星系服从几个标度关系,这是事先没有预料到的。形成的星系有一个紧凑的凸起和磁盘呈指数下降的表面质量密度分布和尺度长度与观察到的星系一致,和垂直的恒星质量分布与不同的指数分布(薄和厚盘)。因此,这项工作首次表明,具有气体和恒星指数分布的盘状星系是MOND中坍缩气体云的一般结果。这些模型有轻微的恒星角动量缺乏,因为他们有点紧凑的恒星隆起,这是连接到简单的初始条件和可以忽略不计的气体吸积。我们还分析了如何增加更复杂的重子物理改变模型的主要结果属性,并发现这是可以忽略不计,所以在Milgromian框架。

英文摘要:

The formation and evolution of galaxies is highly dependent on the dynamics of stars and gas, which is governed by the underlying law of gravity. To investigate how the formation and evolution of galaxies takes place in Milgromian gravity (MOND), we present full hydrodynamical simulations with the Phantom of Ramses (POR) code. These are the first-ever galaxy formation simulations done in MOND with detailed hydrodynamics, including star formation, stellar feedback, radiative transfer and supernovae. These models start from simplified initial conditions, in the form of isolated, rotating gas spheres in the early Universe. These collapse and form late-type galaxies obeying several scaling relations, which was not a priori expected. The formed galaxies have a compact bulge and a disk with exponentially decreasing surface mass density profiles and scale lengths consistent with observed galaxies, and vertical stellar mass distributions with distinct exponential profiles (thin and thick disk). This work thus shows for the first time that disk galaxies with exponential profiles in both gas and stars are a generic outcome of collapsing gas clouds in MOND. These models have a slight lack of stellar angular momentum because of their somewhat compact stellar bulge, which is connected to the simple initial conditions and the negligible later gas accretion. We also analyse how the addition of more complex baryonic physics changes the main resulting properties of the models and find this to be negligibly so in the Milgromian framework.

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