Periodic Reporting for period 5 - FIRST LIGHT (Early Star-Forming Galaxies and Cosmic Reionisation)
Reporting period: 2021-10-01 to 2023-09-30
‘First Light’ refers to the period when the universe emerged from darkness and the first stars and galaxies were born. At this time the universe became bathed in ultraviolet light and dark clouds composed primarily of hydrogen were ionised into their constituent protons and electrons, a transition termed ‘cosmic reionisation’. Exploring and determining the physical processes that governed this final uncharted period of cosmic history is the basis of this ERC programme.
Although the universe began in a ‘Big Bang’ 13.8 billion years ago, the birth of starlight 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 great public appeal and the quest for the earliest galaxies receives widespread media coverage. Such astronomical discoveries regularly inspire young people to enter STEM-based careers.
The programme is observational in nature, exploiting access to the world’s powerful telescopes, aided with a theoretical component based on state-of-the-art simulations. To accelerate the research, international collaborations are established with 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 form to one fully ionised?
(ii) Were hot stars in early galaxies the main source of ionising radiation or was there a contribution from radiation emanating from massive black holes?
(iii) Planning and exploiting the newly-available James Webb Space Telescope, can examples of the ‘first generation’ sources be found verified via their pristine chemical composition?
These questions were proposed in the 2014 proposal and excellent progress has been made as reported below.
Although the universe began in a ‘Big Bang’ 13.8 billion years ago, the birth of starlight 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 great public appeal and the quest for the earliest galaxies receives widespread media coverage. Such astronomical discoveries regularly inspire young people to enter STEM-based careers.
The programme is observational in nature, exploiting access to the world’s powerful telescopes, aided with a theoretical component based on state-of-the-art simulations. To accelerate the research, international collaborations are established with 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 form to one fully ionised?
(ii) Were hot stars in early galaxies the main source of ionising radiation or was there a contribution from radiation emanating from massive black holes?
(iii) Planning and exploiting the newly-available James Webb Space Telescope, can examples of the ‘first generation’ sources be found verified via their pristine chemical composition?
These questions were proposed in the 2014 proposal and excellent progress has been made as reported below.
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.
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.
Referring to the highlights above:
(i) represented the most distant dust detection at the time and remains one of the most significant ALMA achievements in this field in the last decade,
(ii) heralded a major search for the signatures of black holes in the reionisation era, which has developed into a major endeavour with JWST,
(iii) quantifying the amount of leaking radiation from galaxies remains an outstanding challenge in observational astronomy and the team’s work in the area is one of the most cited,
(iv) the team developed a novel and widely-acclaimed method for addressing statistically how feeble galaxies govern the reionisation process
(v) the team provided the first meaningful estimate of when ‘first light’ occurred and their predictions of the visibility of galaxies beyond HST’s horizon were soon verified with JWST.
In each highlight (and others), the First Light team has maintained an innovative and widely-respected research effort via 93 refereed scientific articles. In the final year the team secured nearly 1000 hours of observing time with JWST which will continue to keep them at the forefront for the next few years.
(i) represented the most distant dust detection at the time and remains one of the most significant ALMA achievements in this field in the last decade,
(ii) heralded a major search for the signatures of black holes in the reionisation era, which has developed into a major endeavour with JWST,
(iii) quantifying the amount of leaking radiation from galaxies remains an outstanding challenge in observational astronomy and the team’s work in the area is one of the most cited,
(iv) the team developed a novel and widely-acclaimed method for addressing statistically how feeble galaxies govern the reionisation process
(v) the team provided the first meaningful estimate of when ‘first light’ occurred and their predictions of the visibility of galaxies beyond HST’s horizon were soon verified with JWST.
In each highlight (and others), the First Light team has maintained an innovative and widely-respected research effort via 93 refereed scientific articles. In the final year the team secured nearly 1000 hours of observing time with JWST which will continue to keep them at the forefront for the next few years.