PROFESSOR

The sources of reionization

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 Obiettivo del progetto (Objective)

'The first sources of ionizing radiation formed just a few hundred million years after the Big Bang, when the Universe was only a small fraction of its present age. Their energy transformed the previously cold and neutral gas that filled intergalactic space into the hot and ionized cosmic plasma we observe today. This transformation is called reionization, a key epoch in the history of galaxy formation.

The European Union is making substantial investments into a new generation of telescopes that are, for the first time, powerful enough to see into and beyond the epoch of reionization. The European Extremely Large Telescope and the James Webb Space Telescope will hunt for the light from the hitherto undetected, most distant galaxies. The Low Frequency Array will detect the 21 cm signal from neutral hydrogen and map out the ionization history of the cosmic gas in space and time. The close advent of these and other telescopes creates an urgent need for improving the current theories of reionization.

One of the most pressing unsolved questions regards the nature of the ionizing sources. Past observational and theoretical efforts have identified the stars in the first galaxies as one of the most likely sources of reionization. However, a conclusive assessment stands still out, as do answers to many other open questions: Which galaxies were most important in driving reionization, and why? Were ionizing sources other than stars at play, such as the first black holes? What can we expect the upcoming observations to tell us about structure formation at these early times?

The proposed research will approach these and other essential issues by means of accurate radiation-hydrodynamical simulations of the Universe at large and small scales. It will provide the firm theoretical background needed for the interpretation of observations with the upcoming telescopes, and support and advance the theoretical and observational programmes of the European Union in this field.'

Introduzione (Teaser)

The first generation of galaxies marked with their formation the end of our Universe's dark ages and the beginning of the epoch of reionisation. This transition to a new era has been unravelled by EU-funded scientists through the largest, to date, simulations of the transformation of the intergalactic medium from neutral to ionised.

Descrizione progetto (Article)

The epoch of reionisation is related to many open questions in astrophysics, such as the properties of the first galaxies that drove the ionisation of cosmic gas and the formation of metal-poor stars. Uncovering this process will have far-reaching implications on the study of the evolution of structure in the early Universe.

Substantial observational efforts are currently under way to understand the physical processes that triggered this epoch and governed ramifications on subsequent structure formation. But, observational support for the proposed scenarios is still very scarce.

Scientists working on the EU-funded project PROFESSOR (The sources of reionization) pursued a new numerical approach to simulate the reionisation process. The simulations followed the assembly of gas in the first galaxies and the formation of metal-poor stars inside them.

These objects emitted ultraviolet radiation that carved out ionised regions around them. After a sufficient number of ionising sources had formed, hydrogen in the Universe became fully ionised. The scientists employed the transport of photons in cones (TRAPHIC) code to simulate the propagation of ionising radiation.

TRAPHIC was implemented for radiation-hydrodynamical simulations tracing radiation over a large range of scales and a large number of ionising sources. The simulations were executed on the Supermuc supercomputer at the Leibniz RechenzentrumGarching.

The execution of some of the largest and most detailed simulations of reionisation to date revealed key physical processes that impacted the formation of galaxies and the evolution of reionisation. The results of the PROFESSOR project are expected to contribute to the design of future observational campaigns and interpretation of the data collected.