论文标题

圆盘星系中分子云的湍流驱动参数

The turbulence driving parameter of molecular clouds in disc galaxies

论文作者

Körtgen, Bastian

论文摘要

超音速湍流在星系中分子云和恒星的形成过程中起关键作用。但是,关于速度场中压缩和螺线管模式的比例如何随着时间的流逝而演变,以及它如何依赖于分子云或银河系环境的特性,知之甚少。在这项工作中,我们进行了椎间盘星系的磁性水力学模拟,并研究了云层集合的湍流驱动参数的时间演变。我们发现,时间平均的湍流驱动参数对云在银河系中的位置不敏感。 $ b \ sim0.5-0.7 $发现合奏平均驾驶参数相当压缩,表明几乎与时间无关的全球星形形成属性。但是,每个云都显示出高度波动的驱动参数,这将强烈影响云的恒星形成率。我们发现,湍流驾驶的模式只能在少数Myr之内迅速变化,从螺线管到压缩,反之亦然。我们将这些更改归因于云冲突,以及与环境中云或过度残基的潮汐相互作用。最后,我们发现流体动力学和最初磁性磁性的星系之间的平均驾驶参数没有显着差异。但是,磁场倾向于减少驱动参数的总体波动。人们认为,平均驾驶及其不确定性与太阳邻居云的湍流驾驶模式上的最新限制一致。

Supersonic turbulence plays a pivotal role during the formation of molecular clouds and stars in galaxies. However, little is known about how the fraction of compressive and solenoidal modes in the velocity field evolves over time and how it depends on properties of the molecular cloud or the galactic environment. In this work, we carry out magnetohydrodynamical simulations of disc galaxies and study the time evolution of the turbulence driving parameter for an ensemble of clouds. We find that the time-averaged turbulence driving parameter is insensitive to the position of the cloud within the galaxy. The ensemble-averaged driving parameter is found to be rather compressive with $b\sim0.5-0.7$, indicating almost time-independent global star formation properties. However, each individual cloud shows a highly fluctuating driving parameter, which would strongly affect the cloud's star formation rate. We find that the mode of turbulence driving can rapidly change within only a few Myr, both from solenoidal to compressive and vice versa. We attribute these changes to cloud collisions and to tidal interactions with clouds or overdensities in the environment. Last, we find no significant differences in the average driving parameter between hydrodynamic and initially strongly magnetised galaxies. However, the magnetic field tends to reduce the overall fluctuation of the driving parameter. The average driving as well as its uncertainty are seen to be in agreement with recent constraints on the turbulence driving mode for solar neighbourhood clouds.

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