We study the time evolution of molecular clouds across three Milky Way-like isolated disc galaxy simulations at a temporal resolution of 1 Myr and at a range of spatial resolutions spanning two orders of magnitude in spatial scale from ∼10 pc up to ∼1 kpc. The cloud evolution networks generated at the highest spatial resolution contain a cumulative total of ∼80 000 separate molecular clouds in different galactic–dynamical environments. We find that clouds undergo mergers at a rate proportional to the crossing time between their centroids, but that their physical properties are largely insensitive to these interactions. Below the gas–disc scale height, the cloud lifetime τlife obeys a scaling relation of the form τlife∝ℓ−0.3 with the cloud size ℓ, consistent with over-densities that collapse, form stars, and are dispersed by stellar feedback. Above the disc scale height, these self-gravitating regions are no longer resolved, so the scaling relation flattens to a constant value of ∼13 Myr, consistent with the turbulent crossing time of the gas disc, as observed in nearby disc galaxies.

中文翻译：

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类银河系中分子云寿命的标度关系

我们研究了三个类银河系孤立盘星系模拟中分子云的时间演化，时间分辨率为 1 Myr，空间分辨率范围跨越两个数量级，空间尺度从~10 pc 到~1 kpc。以最高空间分辨率生成的云演化网络在不同的星系动力学环境中累计包含约 80 000 个独立的分子云。我们发现云以与其质心之间的交叉时间成正比的速度进行合并，但它们的物理特性很大程度上对这些相互作用不敏感。在气盘尺度高度以下，云寿命 τlife 遵循 τlife∝ℓ−0.3 与云大小 ℓ 形式的标度关系，与坍缩、形成恒星并通过恒星反馈分散的过密度一致。在盘尺度高度之上，这些自引力区域不再被解析，因此尺度关系变平至~13 Myr的恒定值，与在附近盘星系中观察到的气体盘的湍流穿越时间一致。