Understanding the link between cloud morphology and massive core formation

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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.