河外星系恒星形成的物理规律探讨

Star formation laws in galaxies near and far

冷气体(T<20 K)是星系中恒星形成(SF)的原料,冷气体随引力塌缩成致密分子云核并终将继续塌缩转变成SF到恒星,而SF反馈又推动着星系的形成和演化.详细了解气体的性质,描绘SF和星系的物理关联以及SF对星系的反馈等,是当今极为重要的关键研究.本文主要总结了河外星系中SF的物理规律,探讨了SF与冷气体的相关关系,特别是随着对SF的进一步物理认识,归纳了我们对SF与致密气体关系的系列相关研究,从河外星系整体的研究到对近邻星系空间分解以及与银河系内致密云核的跨度10个数量级的关系;甚至是对更高密度的致密气体,从星系整体到近邻星系空间分解以及河内致密云核的跨度10个数量级的线性相关关系,并指出在ALMA时代SF研究方向的未来发展前景.JCMT的大项目MALATANG提供了对极高密度致密分子气体在近邻星系中大规模分布和SF的认识,了解在星系的中心和更广阔的漩涡盘区各种不同气体状态与致密分子气体和SF之间的物理关联,以及SF和致密分子气体在不同物理尺度上的联系等.随着ALMA/NOEMA的观测推进以及下一代望远镜的投入,有望最终获得不论是遥远或近邻星系从分子云尺度到星系局部、整体各个不同物理尺度上对致密气体和SF的物理性质和规律、多谱线诊断和星系局部SF效率等前沿问题的突破性认识.

Cold gas is the raw material for star formation(SF)in galaxies.Owing to gravitational force,cold gas collapses into dense molecular cloud cores and will eventually continue to collapse and transform into stars.Moreover,SF feedback drives the formation and evolution of galaxies.A detailed understanding of the properties of molecular gas,the description of the physical relationship between SF and galaxies,and SF feedback in galaxies are extremely important studies today.Herein,we only summarize the physical laws of SF in extragalactic galaxies and discuss the relationship between SF and cold gas.In particular,with further physical understanding of star formation,we will summarize our series of related studies on the relationship between SF and dense molecular gas.From the overall global study of entire galaxies,distant external galaxies,and the spatially resolved decomposition of nearby galaxies down to the Galactic dense cloud cores,the linear relationship is valid with a span of 10 orders of magnitude.At even higher densities traced by higher-J rotation ladders of dense gas tracers,this 10-orders-of-magnitude correlation is again tightly maintained from entire galaxies to the spatial decomposition of the denser gas in nearby galaxies,spanning further with the Galactic dense cloud cores.We further discuss future development prospects of this research direction in the Atacama Large Millimeter/submillimeter Array(ALMA)era.The James Clerk Maxwell Telescope large project MALATANG provides an understanding of the large-scale distribution of extremely dense and warm molecular gas in nearby galaxies and probes the relationships among the various gas phases,the dense molecular gas,and SF in the centers of the galaxies and most of the inner spiral disks,ultimately elucidating the physical connection in the relationship between SF and dense molecular gas on different physical scales.With the advancement of ALMA/NOrthern Extended Millimeter Array observations and the investment in next-generation telescopes,we expect to finally obtain the physical properties and laws of dense molecular gas and SF on different physical scales,from the molecular cloud scale to different regions in galaxies(distant and/or nearby galaxies).Eventually,a breakthrough understanding of contemporary issues,such as multispectral diagnosis and local SF efficiency of galaxies,will be in sight.