Understanding the link between cloud morphology and massive core formation

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.

The research conducted in this project does not have any direct impact in the commercial private sector. Its main impact is on Education, in a broad sense. Research in astronomy is a fantastic tool to catch the interests of the population, youngsters or adults, men or women coming from any kind of social background. Through this interest it becomes possible to trigger even deeper curiosity for knowledge, and teach people fundamental sciences such as physics/chemistry/mathematics/biology. In the long term, this will contribute to rise the nation's knowledge/culture, and possibly help increasing the fraction of the UK population going to Higher Education, which in the end could have an impact on the british economy as a whole.

For the PDRA who will work on the project will develop (or enhance) his communication skills, writing skills computational skills, problem-solving skills. All these are transferable skills which, in case he/she does not pursue his/her career in academia, will be very much appreciated in any other employment sectors.

Magazines and newspapers are potential beneficiaries as they might publish articles related to this project. In a similar way as for the Applicant's recent results using the ALMA interferometer (cf Pathways to Impact), the successful outcomes of this new project could be broadly advertised in the news, contributing to the sales of the corresponding medias.

Finally, it is fundamental that scientific excellence is being achieved through the use of these billion pounds instruments that are the Herschel satellite and the ALMA interferometer. Funding agencies need to see that these instruments are well used in order to justify their costs to the tax-payers and their partners. This project can help in that respect.