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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - FIRST LIGHT (Early Star-Forming Galaxies and Cosmic Reionisation)

Teaser

Summary

`First Lightâ€™ refers to the period when the Universe emerged from darkness and the first stars and galaxies were born. At this early time the Universe became bathed in ultraviolet light for the first time and dark clouds composed primarily of hydrogen atoms were gradually ionised into constituent protons and electrons, a transition termed `cosmic reionisationâ€™. Exploring and determining the physical processes that governed this final uncharted period of cosmic history is the basis of Professor Ellisâ€™ ERC programme.

Although the Universe began in a `Big Bangâ€™ 13.8 billion years ago, the birth of starlight explored via this programme is in many ways a more fundamental milestone in cosmic history. All life forms are based on chemical elements synthesised in stars, so the First Light programme directly explores our origins. Astronomy has enormous public appeal and the quest for the earliest galaxies receives widespread media and popular coverage. Numerous studies have shown that such astronomical discoveries regularly inspire young people to enter STEM-based careers.

Ellisâ€™ programme is largely observational in nature, exploiting his access to the worldâ€™s most powerful astronomical telescopes, aided with a theoretical component based on state-of-the-art numerical simulations. To accelerate the research programme, he has established a number of international collaborations with colleagues in Japan and the USA. The programme addresses 3 fundamental questions:

(i) When did First Light occur and over what period did the Universe transition from a neutral (i.e. atomic) form to one that is fully ionised?

(ii) Were hot stars in early galaxies the principal source of ionising radiation or was there a contribution from non-thermal radiation emanating from massive black holes?

(iii) Using the upcoming James Webb Space Telescope can we find examples of the very earliest `first generationâ€™ sources verified via their pristine chemical composition?

Work performed

Professor Ellis arranged to be based at the European Southern Observatory (ESO) for the first two years of the programme in order to ensure rapid familiarisation with European astronomical facilities after his 16 year sojourn in the USA. This has proved highly productive as his group has so far enjoyed a 100% success rate in securing observing time on ESOâ€™s Very Large Telescope (VLT) in Chile. The group has also maintained continued access to the Atacama Large Millimetre Array (ALMA), the Keck and Subaru telescopes in Hawaii, and won a highly competitive programme on the Hubble Space Telescope. Ellis co-leads a proposal for early exploitation of the James Webb Space Telescope (JWST) due for launch in late 2018. As a result, all aspects of the observational programme are ahead of schedule compared to the original proposal. Three postdoctoral associates have been appointed (two in post so far) plus two graduate students (one in post so far) â€“ see Part B 2.3.2 for details. 17 refereed publications have been published and a further 5 are under review (see group web page).

Scientific highlights of the programme thus far include:

- the discovery of dust emission from a source within the reionisation era which promises a new probe of early chemical enrichment from star-forming galaxies, and hence the ability to pinpoint when first light occurred. This result was the subject of an international press release with prominent coverage in the New York Times (see Part B 2.3.2).
- the discovery of spectroscopic signatures suggestive of non-thermal radiation from nuclear black holes in early galaxies providing the first evidence of a contribution from active galactic nuclei to the reionisation process.
demonstration of a productive route for characterising both the nature of the radiation field produced by early galaxies and the fraction of that radiation that can escape into the intergalactic medium. This is a key challenge to addressing how reionisation occurred.

Final results

Exploring the reionisation era is extremely challenging as the sources in question are at the limits accessible with current facilities. The group has maintained its global leadership in this area via the most detailed spectroscopic studies of early galaxies using the worldâ€™s largest telescopes (VLT and Keck). The ALMA highlight above also represents a significant breakthrough; not only is it the most distant detected ALMA source by a wide margin, but it offers a completely new route to pinpointing when galaxies first emerged. Along with these discoveries, Professor Ellis and postdoctoral associate Dr Nicolas Laporte have maintained a strong outreach programme with many public lectures, events in schools and TV documentaries.