CR7 is not alone: a team of super bright galaxies in the early Universe
Astronomers have identified a family of incredible galaxies that could shed further light on the transformation of the early Universe known as the ‘epoch of reionisation’. Dr David Sobral of Lancaster University will present their results on Monday 27 June at the National Astronomy Meeting in Nottingham.
About 150 million years after the Big Bang, some 13 billion years ago, the Universe was completely opaque to high energy ultraviolet light, with neutral hydrogen gas blocking its passage. Astronomers have long realised that this situation ended in the so-called ‘epoch of reionisation’, where ultraviolet light from the earliest stars broke open neutral hydrogen atoms, and could start to travel freely through the cosmos. This reionisation period marks a key transition between the relatively simple early cosmos, with normal matter made up of hydrogen and helium, and the universe as we see it today: transparent on large scales and filled with heavier elements.
In 2015 Sobral led a team that found the first example of a spectacularly bright galaxy within the epoch of reionisation, named Cosmos Redshift 7 or CR7, which may harbour first generation stars. The team also discovered a similar galaxy, MASOSA, which, together with Himiko, discovered by a Japanese team, hinted at a larger population of similar objects, perhaps made up of the earliest stars and/or black holes.
Using the Subaru and Keck telescopes on Hawaii, and the Very Large Telescope in Chile, Sobral and his team, along with a group in the US, have now found more examples of this population. All of the newly found galaxies seem to have a large bubble of ionised gas around them.
Sobral comments: “Stars and black holes in the earliest, brightest galaxies must have pumped out so much ultraviolet light that they quickly broke up hydrogen atoms in the surrounding universe. The fainter galaxies seem to have stayed shrouded from view for a lot longer. Even when they eventually become visible, they show evidence of plenty of opaque material still in place around them.”
“This makes the bright galaxies visible much earlier on in the history of the Universe, allowing us to not only use them to study reionisation itself, but also to study the properties of the very first galaxies and the black holes they may contain”, adds team member Jorryt Matthee, a PhD student at Leiden Observatory.
Sergio Santos is another co-author of the study and will soon be a PhD student at Lancaster University. He adds: “Our results highlight how hard it is to study the small faint sources in the early Universe. The neutral hydrogen gas blocks out some of their light, and because they are not capable of building their own local bubbles as quickly as the bright galaxies, they are much harder to detect.”
With five bright sources now confirmed, and many more expected to follow, CR7 may be part of a ‘team’ of tens to hundreds of thousands of bright galaxies. The fifth (V) galaxy, also discovered by Sobral and his team, takes the name VR7, this time in tribute to the astrophysicist Vera Rubin, who in 1996 became the first woman in over 150 years to win the Gold Medal of the Royal Astronomical Society.
Sobral is now looking forward to continuing his work with the new telescopes that will become available in the next few years. He comments: “What is really surprising is that the galaxies we find are much more numerous than people assumed, and they have a puzzling diversity. When telescopes like the James Webb Space Telescope are up and running, we will be able to take a closer look at these intriguing objects. We have only scratched the surface, and so the next few years will certainly bring fantastic new discoveries.”
For now, astronomers are using the largest existing telescopes on the ground and in space to better assess the composition, size and shape of the new galaxies. Results from this work have and will appear in papers in the journal Monthly Notices of the Royal Astronomical Society.
Dr Robert Massey
Ms Anita Heward
Dr David Sobral
Images and captions
This illustration of reionisation shows a timeline summarising the evolution of the Universe running from left to right, where the Big Bang is on the left and the age of the Universe is about two billion years on the right. It shows how the cosmic “fog" of neutral (uncharged) hydrogen pervading the early Universe is cleared by the first objects to emit radiation. Credit: NASA / CXC / M.Weiss
This artist’s impression shows CR7, a very distant galaxy discovered using ESO’s Very Large Telescope. It is by far the brightest galaxy yet found in the early Universe and there is strong evidence that examples of the first generation of stars lurk within it. These massive, brilliant, and previously purely theoretical objects were the creators of the first heavy elements in history — the elements necessary to forge the stars around us today, the planets that orbit them, and life as we know it. This newly found galaxy is three times brighter than the brightest distant galaxy known up to now. Credit: ESO / M. Kornmesser
The full team consists of David Sobral (Lancaster), Sergio Santos (Lancaster), Jorryt Matthee (Leiden), and Behnam Darvish (Caltech).
The initial discovery of a much larger population of bright sources within the epoch of reionisation is presented in Matthee, Sobral, Santos et al. 2015, published in Monthly Notices of the Royal Astronomical Society (http://mnras.oxfordjournals.org/content/451/1/400).
The discoveries of CR7 and MASOSA are described in Sobral, Matthee, Darvish et al. 2015, published in The Astrophysical Journal. Since this paper, several others have been submitted to or published in Monthly Notices of the Royal Astronomical Society to attempt to model and explain the unique nature of the CR7 galaxy.
The new results on the evolution of the number densities of bright sources into reionisation are to be published in Monthly Notices of the Royal Astronomical Society in Santos, Sobral & Matthee 2016. Follow-up observations leading to the confirmation of VR7 and other bright Lyman-alpha emitters are to be presented in forthcoming papers.
The discovery of Himiko, initially thought to be one-of-a-kind, was presented by e.g. Ouchi et al. 2013. Recently, an independent US/Hawaii-based team has discovered a CR7-like galaxy, named COLA-1; results will be published in Astrophysical Journal Letters in Hu et al. 2016.
Notes for editors
The RAS National Astronomy Meeting 2016 (NAM 2016) takes place this year at the University of Nottingham from 27 June to 1 July. NAM 2016 brings together more than 550 space scientists and astronomers to discuss the latest research in their respective fields. The conference is principally sponsored by the Royal Astronomical Society and the Science and Technology Facilities Council. Follow the conference on Twitter via @rasnam2016
The University of Nottingham has 43,000 students and is ‘the nearest Britain has to a truly global university, with a “distinct” approach to internationalisation, which rests on those full-scale campuses in China and Malaysia, as well as a large presence in its home city.’ (Times Good University Guide 2016). It is also one of the most popular universities in the UK among graduate employers and the winner of ‘Outstanding Support for Early Career Researchers’ at the Times Higher Education Awards 2015. It is ranked in the world’s top 75 by the QS World University Rankings 2015/16, and 8th in the UK by research power according to the Research Excellence Framework 2014. It has been voted the world’s greenest campus for four years running, according to Greenmetrics Ranking of World Universities.
Impact: The Nottingham Campaign, its biggest-ever fundraising campaign, is delivering the University’s vision to change lives, tackle global issues and shape the future.
The Science and Technology Facilities Council (STFC) is keeping the UK at the forefront of international science and has a broad science portfolio and works with the academic and industrial communities to share its expertise in materials science, space and ground-based astronomy technologies, laser science, microelectronics, wafer scale manufacturing, particle and nuclear physics, alternative energy production, radio communications and radar. STFC's Astronomy and Space Science programme provides support for a wide range of facilities, research groups and individuals in order to investigate some of the highest priority questions in astrophysics, cosmology and solar system science. STFC's astronomy and space science programme is delivered through grant funding for research activities, and also through support of technical activities at STFC's UK Astronomy Technology Centre and RAL Space at the Rutherford Appleton Laboratory. STFC also supports UK astronomy through the international European Southern Observatory. Follow STFC on Twitter via @stfc_matters
The Royal Astronomical Society (RAS), founded in 1820, encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science. The RAS organizes scientific meetings, publishes international research and review journals, recognizes outstanding achievements by the award of medals and prizes, maintains an extensive library, supports education through grants and outreach activities and represents UK astronomy nationally and internationally. Its more than 4000 members (Fellows), a third based overseas, include scientific researchers in universities, observatories and laboratories as well as historians of astronomy and others.
The RAS accepts papers for its journals based on the principle of peer review, in which fellow experts on the editorial boards accept the paper as worth considering. The Society issues press releases based on a similar principle, but the organisations and scientists concerned have overall responsibility for their content.
Follow the RAS on Twitter