Understanding the link between cloud morphology and massive core formation

大质量恒星(质量10毫升)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有助于我们更好地理解可观测的宇宙，也有助于我们构建一幅所有质量的恒星形成的图景，因为作为极端物体，大质量恒星对恒星形成理论的约束最大。现在人们认为，太阳型恒星的直接祖先，即所谓的核心，主要是在低质量、引力不稳定的长灯丝中形成的。低质量核心的质量，以及在其中形成的恒星，都是由这种局部碎裂过程决定的。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塌缩云的中心形成的。在这张图片中，最终进入大质量核心的气体来自一个大得多的质量储藏室，整个云层的大小。局部碎裂肯定不是形成这种极端核心的主要机制，这与目前提出的形成低质量核心的机制形成鲜明对比。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不同有关。事实上，初始云形态(即云的纵横比)可能是确定核心/恒星质量的一个关键参数，因为它在给定密度下确定了云的动态时间尺度和恒星吸积时间尺度之间的相对时间尺度。拉长的细丝将碎裂，并倾向于在细丝在全球范围内坍塌很久之前形成低质量恒星，而球状云团将在类似的时间尺度上做到这两点。该项目旨在通过探测一组原始云的致密气体运动学来研究云形态在块状核心形成中的作用。根据云的初始纵横比、质量和密度的函数，云的运动学和核心属性预计会有显著的差异。对来自单碟式望远镜和干涉仪的大量观测数据的分析将使我们能够确定形成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.