The cold interstellar medium (ISM) plays a central role in the galaxy evolution process. It is the reservoir that fuels galaxy growth via star formation, the repository of material formed by these stars, and a sensitive tracer of internal and external processes that affect entire galaxies. Consequently, significant efforts have gone into systematic surveys of the cold ISM of the galaxies in the local Universe. This review discusses the resulting network of scaling relations connecting the atomic and molecular gas masses of galaxies with their other global properties (stellar masses, morphologies, metallicities, star-formation activity…) and their implications for our understanding of galaxy evolution. Key take-home messages are as follows: ▪ From a gas perspective, there are three main factors that determine the star-formation rate of a galaxy: the total mass of its cold ISM, how much of that gas is molecular, and the rate at which any molecular gas is converted into stars. All three of these factors vary systematically across the local galaxy population. ▪ The shape and scatter of both the star-formation main sequence and the mass–metallicity relation are deeply linked to the availability of atomic and molecular gas. ▪ Future progress will come from expanding our exploration of scaling relations into new parameter space (in particular, the regime of dwarf galaxies), better connecting the cold ISM of large samples of galaxies with the environment that feeds them (the circumgalactic medium, in particular), and understanding the impact of these large scales on the efficiency of the star-formation process on molecular cloud scales.

中文翻译：

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本宇宙中星系的寒冷星际介质


冷星际介质 （ISM） 在星系演化过程中起着核心作用。它是通过恒星形成为星系生长提供燃料的储存库，是这些恒星形成的物质库，也是影响整个星系的内部和外部过程的敏感示踪剂。因此，人们投入了大量精力对本地宇宙中星系的冷 ISM 进行系统调查。本文讨论了将星系的原子和分子气体质量与其其他全局特性（恒星质量、形态、金属丰度、恒星形成活动等）联系起来的缩放关系网络，以及它们对我们理解星系演化的影响。关键的信息如下：▪从气体的角度来看，决定星系恒星形成速率的主要因素有三个：其冷 ISM 的总质量、气体中有多少是分子的，以及任何分子气体转化为恒星的速度。所有这三个因素在当地星系种群中都系统性地变化。▪ 恒星形成主序列的形状和散射以及质量-金属丰度关系都与原子和分子气体的可用性密切相关。▪ 未来的进展将来自于将我们对缩放关系的探索扩展到新的参数空间（特别是矮星系的机制），更好地将大样本星系的冷 ISM 与喂养它们的环境（特别是银河系周围介质）联系起来，并了解这些大尺度对分子云尺度上恒星形成过程效率的影响。