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Gas-rich baby galaxies set the early Universe alight

ARC Centre of Excellence for All Sky Astrophysics in Three Dimensions (ASTRO-3D) 4 mins read
Images of a distant extreme emission line galaxy. Seen by James Webb Space Telescope (left) and Hubble Space Telescope (right). This comparison highlights the clarity of JWST images.

EMBARGOED UNTIL: 0500 AEDT Tuesday 7 November 2023

New images from the James Webb Space Telescope (JWST) have helped Australian astronomers unlock secrets of how infant galaxies started an explosion of star formation in the very early Universe.

Some early galaxies were abundant with a gas that glowed so bright it outshone emerging stars. In research published today, astronomers have now discovered just how prevalent these bright galaxies were some 12 billion years ago.

Images from the JWST have shown that almost 90% of the galaxies in the early universe had this glowing gas, producing so-called ‘extreme emission line features’.

“The stars in these young galaxies were remarkable, producing just the right amount of radiation to excite the surrounding gas. This gas, in turn, shone even brighter than the stars themselves,” says Dr Anshu Gupta from the ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D) and the Curtin University node of the International Centre for Radio Astronomy Research (ICRAR), the lead author of a paper describing the discovery.

“Until now, it was challenging to understand how these galaxies were able to accumulate so much gas. Our findings suggest that each of these galaxies had at least one close neighbouring galaxy. The interaction between these galaxies would cause gas to cool and trigger an intense episode of star formation, resulting in this extreme emission feature.”

The discovery is a graphic example of the unparalleled clarity the JWST telescope provides in studying the early Universe.

“The data quality from the James Webb telescope is exceptional,” says Dr Gupta. “It has the depth and resolution needed to see the neighbours and environment around early galaxies from when the Universe was only 2 billion years old. With this detail we were able to see a marked difference in the number of neighbours between galaxies with the extreme emission features and those without.”

Previously we struggled to get a clear picture of galaxies from around 2 billion years of the Universe’s age. As many stars had yet to form, the task was made more difficult with many fewer galaxies to focus on.

“Prior to JWST, we could only really get a picture of really massive galaxies, most of which are in really dense clusters making them harder to study,” Dr Gupta says. “With the technology available then, we couldn’t observe 95% of the galaxies we used in this study. The James Webb telescope has revolutionised our work.”

The discovery has proven previous assumptions, says fellow author Associate Director Tran, ASTRO 3D and the Center of Astrophysics, Harvard and Smithsonian. “We suspected that these extreme galaxies are signposts of intense interactions in the early universe, but only with the sharp eyes of JWST could we confirm our hunch,” she says.

The research relied on data obtained as part of the JWST Advanced Deep Extragalactic Survey (JADES) survey, which is exploring the Universe of the earliest galaxies with deep infrared imaging and multi-object spectroscopy. It opens the way for further insights.

"What’s really exciting about this piece is that we see emission line similarities between the very first galaxies to galaxies that formed more recently and are easier to measure. This means we now have more ways to answer questions about the early universe, a period that is technically very hard to study,” says second author, Ravi Jaiswar, a PhD student at Curtin University/ICRAR and ASTRO 3D.

“This research is core to the work of our Galaxy Evolution Program. By understanding what early galaxies look like, we can build on answering questions on the origin of the elements that make up our everything in our everyday life here on Earth.” says Professor Emma Ryan-Weber, Director of ASTRO 3D.


Paper Details

Journal: The Astrophysical Journal (approved), released on pre-print on Axriv

MOSEL survey: JWST reveals major mergers/strong interactions drive the extreme emission lines in the early universe 

Anshu Gupta,1,2 Ravi Jaiswar,1,2 Vicente Rodriguez-Gomez,3,4 Ben Forrest,5 Kim-Vy Tran,6,2,7 Themiya Nanayakkara,8,2 Anishya Harshan,9 Elisabete da Cunha,10,2 Glenn G. Kacprzak,11,2 and Michaela Hirschmann12,13

1International Centre for Radio Astronomy Research (ICRAR), Curtin University, Bentley WA, Australia
2ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), Australia
3Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218, USA
4Instituto de Radioastronomía y Astrofísica, Universidad Nacional Autónoma de México, A.P. 72-3, 58089 Morelia, Mexico 
5Department of Physics and Astronomy, University of California Davis, One Shields Avenue, Davis, CA, 95616, USA
6School of Physics, University of New South Wales, Sydney, NSW 2052, Australia
7Center for Astrophysics | Harvard & Smithsonian, Cambridge, MA
8Centre for Astrophysics and Supercomputing, Swinburne University of Technology, Hawthorn, VIC 3122, Australia
9University of Ljubljana, Department of Mathematics and Physics, Jadranska ulica 19, SI-1000 Ljubljana, Slovenia
10International Centre for Radio Astronomy Research, University of Western Australia, 35 Stirling Hwy, Crawley, WA 6009, Australia
11Swinburne University of Technology, Hawthorn, VIC 3122, Australia
12Institute of Physics, GalSpec, Ecole Polytechnique Federale de Lausanne, Observatoire de Sauverny, Chemin Pegasi 51, 1290 Versoix, Switzerland 
13INAF, Astronomical Observatory of Trieste, Via Tiepolo 11, 34131 Trieste, Italy 


Extreme emission line galaxies (EELGs), where nebular emissions contribute 30-40% of the flux in certain photometric bands, are ubiquitous in the early universe (𝑧 > 6). We utilise deep NIRCam imaging from the JWST Advanced Deep Extragalactic Survey (JADES) survey to investigate the properties of companions (projected distance < 40𝑘𝑝𝑐, |𝑑𝑣| < 10,000km/s) around EELGs at 𝑧  3. Tests with TNG100 simulation reveal that nearly all galaxies will merge with at least one companion selected using similar parameters at 𝑧 = 3. The median mass ratio of the most massive companion and the total mass ratio of all companions around EELGs is more than 10 times higher the control sample. Even after comparing with a stellar mass-matched control sample, EELGs have three-to-five times higher mass ratios of the brightest companion and total mass ratio of all companions. Our measurements suggest that EELGs are more likely to be experiencing strong interactions or undergoing major mergers irrespective of their stellar mass. We suspect that gas cooling induced by strong interactions and/or major mergers could be triggering the extreme emission lines, and the increased merger rate might be responsible for the over-abundance of EELGs at 𝑧 > 6. 


About us:


The ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D) is a $40 million Research Centre of Excellence funded by the Australian Research Council (ARC) and nine collaborating Australian universities – The Australian National University, The University of Sydney, The University of Melbourne, Swinburne University of Technology, The University of Western Australia, Curtin University, Macquarie University, The University of New South Wales, and Monash University.


The International Centre for Radio Astronomy Research (ICRAR) is a joint venture between Curtin University and The University of Western Australia with support and funding from the State Government of Western Australia.


Contact details:

Tom Carruthers,, +61 404 404 026

High resolution images are available at


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