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COSMICISM Report Summary

Project ID: 321302
Funded under: FP7-IDEAS-ERC
Country: United Kingdom

Final Report Summary - COSMICISM (Characterising the interstellar medium of bright, lensed, star-forming galaxies across cosmic time)

Molecular gas is the fuel from which stars are formed. It can sometimes also be dragged down onto super-massive black holes in the centres of galaxies. The impact on the physical properties of the molecular gas of star formation and the accretion of gas onto black holes are overarching themes in astrophysics. In particular, we would like to know whether these processes influence the relative fractions of low- and high-mass stars that are created in a galaxy, something astronomers call the "initial mass function". This has a profound effect on how a galaxy evolves and on how many stars and planets it may contain in later life.

We are entering an era where computer simulations of turbulent molecular gas can be informed and constrained by astronomical observations of such gas using the latest generation of telescopes. These are so powerful that they can detect galaxies inconceivably distant from Earth, seen just as they were when the light seen by these telescopes left them, billions of years ago. The COSMICISM project is investigating, both theoretically and observationally, the impact of star formation that is driven by galaxies colliding and merging, during a vital period in cosmic history, around twice the age of the Earth ago, when many of today’s stars were formed.

It is at this crucial cosmic epoch that we must study the laws of star formation, and turbulence-regulated aspects of star formation, looking for possibly dramatic differences in the initial conditions of star formation, and the different fractions of low- and high-mass stars these may impose.

These younger galaxies were significantly more gas-rich and turbulent than the most intensely starbursting galaxies in today's Universe - those observed close to the Milky Way, where our Sun is situated. They had different fragmentation histories and more intense star formation, and so cosmic rays were more prevalent. When searching for a high ratio of high- to low-mass stars, these intensely starbursting distant galaxies should yield cleaner signatures than nearby starbursts (which we see more-or-less as they are today, in their old age), because the much older nearby starbursts may have undergone subsequent periods of ordinary star formation, thereby diluting such signatures.

These signatures are terrifically faint - impossible to discern with even our most powerful telescopes, with the most sensitive instruments available today, in space and on high mountain sites around the world. The COSMICISM project is therefore exploiting distant starbursts that have been highly magnified by chance alignments with other galaxies along our line of sight - so-called gravitational lensing - to gather the required diagnostics.

At this level of sophistication, the analysis of the gas in distant galaxies - so distant that the light from them was emitted before the Earth even existed - begins to be comparable to that possible in the galaxies in our local neighbourhood. The relative abundance of different chemical elements will reveal the dominant form of nucleosynthesis enriching their gas reservoirs - is it the nucleosynthesis typically seen in high-mass stars, or that seen in low-mass stars? The answer has important cosmological consequences. The COSMICISM project has been the vehicle by which mankind better understands a crucial component of our ever-puzzling Universe.

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