Professor Ellis was based at the European Southern Observatory (ESO) Headquarters in Germany for the first two years of the programme to ensure rapid familiarisation with European astronomical facilities after 16 years in the USA. This proved effective as his group secured much observing time on ESO’s Very Large Telescope (VLT) in Chile. In September 2017, he relocated to University College London (UCL).
The programme combines challenging and innovative observations of distant early galaxies and analogues at intermediate ‘look-back times,’ with simulations aimed to interpret the results in the context of models of galaxy formation and evolution. Ground-based observations exploit the ESO VLT, the Atacama Large Millimetre Array (ALMA) and the Subaru and twin Keck telescopes in Hawaii. In space, ambitious campaigns are undertaken on the Hubble Space Telescope (HST) and the award was given a no-cost extension to include analyses of data from the recently-launched James Webb Space Telescope (JWST). This area of research is highly competitive with as many as a dozen research groups seeking observing time worldwide. Professor Ellis’ group has remained at the forefront in this area as evidenced by the success in securing observing time, invitations to give plenary talks at international conferences and numerous distinguished prizes at itemised below.
During the 8 year programme, Ellis worked with 6 postdoctoral associates, 4 graduate students and collaborators in the USA and Japan. The team published 93 refereed articles (see group web page).
Scientific highlights include:
(i) 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,
(ii) discovery of spectroscopic signatures indicative of non-thermal radiation from black holes in early galaxies providing the first evidence for such a contribution to the reionisation process,
(iii) detailed analysis of a large sample of intermediate redshift analogues of faint sources in the reionisation era. As well as characterising the nature of their stellar radiation, Hubble Space Telescope imaging reveals a sizeable fraction show leaking ionising radiation. This work provides the first quantitative evidence that metal-poor galaxies made a major contribution to the reionisation process,
(iv) demonstration of a new way of determining the amount of radiation that can escape into the intergalactic medium by correlating their spatial distribution with the fluctuating hydrogen absorption seen in background sources.
(v) a detailed analysis of the stars and gas in very early galaxies indicating they formed 300 million years earlier, even at this remote epoch. The team predicted galaxies formed beyond the horizon of observation accessible HST, a result later confirmed with JWST. The remaining challenge will be to locate and recognise chemically-pristine galaxies at first light. Using theoretical simulations the team published an important article on realising this goal with JWST.
For his pioneering work funded by the ERC, Ellis received the Michael Faraday Gold Medal of the Institute of Physics and the Royal Medal of the Royal Society (both represent the respective bodies’ highest award in the physical sciences). In 2023, Ellis also received the Gruber Foundation Prize in Cosmology for “for his numerous contributions in the fields of galaxy evolution, the onset of cosmic dawn and reionization in the high redshift universe, and the detection of the earliest galaxies.”
Ellis has undertaken significant public outreach activities during the award including a popular book based on his discoveries - When Galaxies Were Born: The Quest for Cosmic Dawn (Princeton 2022). He recently gave a public lecture on the first results from JWST to an audience of 1500 at London’s Excel Centre.
