Understanding the link between cloud morphology and massive core formation

大质量恒星通过其巨大的亮度和强大的反馈控制着宇宙中星系的能量收支。尽管它们很重要，但导致大质量恒星形成的机制仍然是一个谜。因此，了解大质量恒星如何积累质量将使我们更好地理解可观测的宇宙，同时也有助于我们构建各种质量恒星形成的图景，因为作为极端物体，大质量恒星对恒星形成理论的限制最大。现在人们认为，太阳型恒星的直接祖先，称为核心，主要形成于低质量、引力不稳定的长细丝中。低质量核心的质量，以及在其中形成的恒星，是由这种局部破碎过程决定的。另一方面，我们最近的ALMA结果表明，大质量恒星形成的核心是在全球坍缩云的中心形成的。在这幅图中，最终形成大质量核心的气体来自一个更大的质量储层，相当于整个星云的大小。局部破碎绝对不是这种极端地核形成的主要机制，这与目前提出的低质量地核形成的理论形成鲜明对比。这些低质量和高质量恒星形成之间的明显差异可能与母云初始条件的差异有关。事实上，初始云形态（即云长宽比）可能是确定核心/恒星质量的关键参数，因为它在给定密度下固定了云的动态时间标度和恒星吸积时间标度之间的相对时间标度。在长丝整体坍塌之前，细长的细丝会断裂并倾向于形成低质量的恒星，而球形云在类似的时间尺度上也会发生这两种情况。这里提出的项目旨在通过探测一组原始云的稠密气体运动学来研究云形态在大质量核心形成中的作用。在云的运动学和核心属性方面，作为云的初始纵横比、质量和密度的函数，预计会有显著的差异。对单碟望远镜和干涉仪的大量观测结果进行分析，将使我们能够确定大质量恒星形成核心的条件。

Massive stars (Mass > 10 Msun) control the energy budget of galaxies in the Universe through their enormous luminosities and powerful feedback. Despite their importance, the mechanisms leading to the formation of massive stars remain a mystery. Understanding how massive stars build up their mass will therefore allow us to better understand the observable Universe, but also help us to build a picture of star formation at all masses since, as extreme objects, massive stars are most constraining for star formation theories.It is now believed that the direct progenitors of solar-type stars, called cores, form predominantly in low-mass, gravitationally unstable, long filaments. The mass of the low-mass cores, and the stars which form in them, is set by this local fragmentation process. On the other hand, our recent ALMA results suggest that massive star forming cores form at the centre of globally collapsing clouds. In this picture the gas ending up in massive cores originate from a much larger mass reservoir the size of the entire cloud. Local fragmentation is definitely not the main mechanism for the formation of such extreme cores, which is in stark contrast with what is currently proposed for the formation of low-mass cores.These apparent differences between low- and high-mass star formation are probably linked to differences in the parental cloud initial conditions. Indeed, initial cloud morphology (i.e. cloud aspect ratio) could be a key parameter in determining the mass of cores/stars as it fixes, at a given density, the relative timescales between the cloud's dynamical timescale and the timescale for star accretion. Elongated filaments will fragment and tend to form low-mass stars long before the filament globally collapses, while spherical clouds will do both on similar timescales. The project proposed here aims to investigate the role of cloud morphology on massive core formation by probing the dense gas kinematics of a set of pristine clouds. Marked differences are expected in terms of cloud's kinematics and core properties as a function of the cloud's initial aspect ratio, mass, and density. The analysis of a large set of observations from both single dish telescopes and interferometers will allow us to establish the conditions under which massive star forming cores can form.