The secrets of 3000 galaxies laid bare

Completion of Australian-led astronomy project sheds light on the evolution of the Universe

The complex mechanics determining how galaxies spin, grow, cluster and die have been revealed following the release of all the data gathered during a massive seven-year Australian-led astronomy research project.

The scientists observed 13 galaxies at a time, building to a total of 3068, using a custom-built instrument called the Sydney-AAO Multi-Object Integral-Field Spectrograph (SAMI), connected to the 4-metre Anglo-Australian Telescope (AAT) at Siding Spring Observatory in New South Wales. The telescope is operated by the Australian National University.

Overseen by the ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), the project used bundles of optical fibres to capture and analyse bands of colours, or spectra, at multiple points in each galaxy.

The results allowed astronomers from around the world to explore how these galaxies interacted with each other, and how they grew, sped up or slowed down over time.

No two galaxies are alike. They have different bulges, haloes, disks and rings. Some are forming new generations of stars, while others haven’t done so for billions of years. And there are powerful feedback loops in them fuelled by supermassive black holes.

“The SAMI survey lets us see the actual internal structures of galaxies, and the results have been surprising,” said lead author Professor Scott Croom from ASTRO 3D and the University of Sydney.

“The sheer size of the SAMI Survey lets us identify similarities as well as differences, so we can move closer to understanding the forces that affect the fortunes of galaxies over their very long lives.”

The survey, which began in 2013, has already formed the basis of dozens of astronomy papers, with several more in preparation. A paper describing the final data release – including, for the first time, details of 888 galaxies within galaxy clusters – was published today on the arxiv pre-print server and in the journal Monthly Notices of the Royal Astronomical Society.

“The nature of galaxies depends both on how massive they are and their environment,” said Professor Croom. 

“For example, they can be lonely in voids, or crowded into the dense heart of galactic clusters, or anywhere in between. The SAMI Survey shows how the internal structure of galaxies is related to their mass and environment at the same time, so we can understand how these things influence each other.”

Research arising from the survey has already revealed several unexpected outcomes.

One group of astronomers showed that the direction of a galaxy’s spin depends on the other galaxies around it, and changes depending on the galaxy’s size.  Another group showed that the amount of rotation a galaxy has is primarily determined by its mass, with little influence from the surrounding environment. A third looked at galaxies that were winding down star-making, and found that for many the process began only a billion years after they drifted into the dense inner-city regions of clusters.

“The SAMI Survey was set up to help us answer some really broad top-level questions about galaxy evolution,” said co-author Dr Matt Owers from Macquarie University in Australia.

“The detailed information we’ve gathered will help us to understand fundamental questions such as: Why do galaxies look different depending on where they live in the Universe? What processes stop galaxies forming new stars and, conversely, what processes drive the formation of new stars? Why do the stars in some galaxies move in a highly ordered rotating disk, while in other galaxies their orbits are randomly oriented?”

Professor Croom added, “The survey is finished now, but by making it all public we hope that the data will continue to bear fruit from many, many years to come.”

Co-author Associate Professor Julia Bryant from ASTRO 3D and the University of Sydney said: “The next steps in this research will make use of a new Australian instrument – which we’ve called Hector – that will start operation in 2021, increasing the detail and number of galaxies that can be observed.”

When fully installed in the AAT, Hector will survey 15,000 galaxies.

The final data release paper has 41 authors, drawn from Australia, Belgium, the US, Germany, Britain, Spain and The Netherlands.

The full data set is available online through Australian Astronomical Optics (AAO) Data Central.

Visuals: caption and credits


Caption: A/Prof Julia Bryant from the University of Sydney inside the SAMI instrument at the top end of the Anglo Australian Telescope.
Credit: Scott Croom/University of Sydney

Video and GIF captions and credits


Title: A SAMI night at the Anglo Australian Telescope
This three-and-a-half minute video shows highlights of researchers adjusting and deploying the SAMI instrument at the Anglo Australian Telescope at Siding Spring University in New South Wales, Australia.
Credit: Ángel R. López-Sánchez (Australian Astronomical Observatory / Macquarie University)
Featuring: Luca Cortese (ICRAR-UWA), Jesse van de Sande (University of Sydney) and Steve Chapman (Night Assistant at the AAT)
SAMI plugger: Ángel R. López-Sánchez (AAO/MQU)
Music: It’s personal (World in Flames, 2011), Celestial Aeon Project.


The SAMI instrument inside the Anglo Australian Telescope being readied for action.
Credit: Ángel R. López-Sánchez (AAO-MQ)


Time lapse of Anglo Australian Telescope, showing the SAMI survey being conducted.
Credit: Ángel R. López-Sánchez (AAO-MQ)


Time lapse of Anglo Australian Telescope, showing the SAMI survey being conducted.
Credit: Ángel R. López-Sánchez (AAO-MQ)

Paper details, authors and affiliations

The SAMI Galaxy Survey: the third and final data release
arxiv URL:

Scott M. Croom 1,2, Matt S. Owers 3,4, Nicholas Scott 1,2, Henry Poetrodjojo 1,2, Brent Groves 5,6,2, Jesse van de Sande 1,2, Tania M. Barone 6,1,2, Luca Cortese 5,2, Francesco D’Eugenio 7, Joss Bland-Hawthorn 1,2, Julia Bryant 1,2, Sree Oh 6,2, Sarah Brough 8,2, James Agostino 9, Sarah Casura 10, Barbara Catinella 5,2, Matthew Colless 6,2, Gerald Cecil 11, Roger L. Davies 12, Michael J. Drinkwater 13, Simon P. Driver 5, Ignacio Ferreras 14,15,16, Caroline Foster 1,2, Amelia Fraser-McKelvie 5,2, Jon Lawrence 17, Sarah K. Leslie 18,2, Jochen Liske 10, Angel R. Lopez-Sanchez, 3,4,2, Nuria P. F. Lorente 17, Rebecca McElroy 1,2, Anne M. Medling 9,2, Danail Obreschkow 5,2, Samuel N. Richards 19, Rob Sharp 6, Sarah M. Sweet 12,2, Dan S. Taranu 20, Edward N. Taylor 21, Edoardo Tescari 22, Adam D. Thomas 6,2, James Tocknell 17, Sam P. Vaughan 1,2

1 Sydney Institute for Astronomy (SIfA), School of Physics, The University of Sydney, NSW, 2006, Australia
2 ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D)
3 Department of Physics and Astronomy, Macquarie University, NSW, 2109, Australia
4 Astronomy, Astrophysics and Astrophotonics Research Centre, Macquarie University, Sydney, NSW 2109, Australia
5 ICRAR, The University of Western Australia, Crawley WA 6009, Australia
6 Research School of Astronomy and Astrophysics, Australian National University, Canberra, ACT 2611, Australia
7 Sterrenkundig Observatorium, Universiteit Gent, Krijgslaan 281 S9, B-9000 Gent, Belgium
8 School of Physics, University of New South Wales, NSW 2052, Australia
9 Ritter Astrophysical Research Center, University of Toledo, Mail Stop 111, Toledo, OH, 43606, United States
10 Hamburger Sternwarte, Universit¨at Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany
11 Dept. Physics and Astronomy University of North Carolina Chapel Hill, NC 27599 USA
12 Astrophysics, Department of Physics, University of Oxford, Denys Wilkinson Building, Keble Rd., Oxford, OX1 3RH, UK.
13 School of Mathematics and Physics, University of Queensland, Brisbane, QLD 4072, Australia
14 Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK
15 Instituto de Astrofisica de Canarias, Calle Via Lactea s/n, E38205 La Laguna, Tenerife, Spain
16 Departamento de Astrofisica, Universidad de La Laguna (ULL), La Laguna, E-38206 Tenerife, Spain
17 Australian Astronomical Optics – Macquarie, Macquarie University, NSW 2109, Australia
18 Leiden Observatory, Leiden University, PO Box 9513, NL-2300 RA Leiden, the Netherlands
19 SOFIA Science Center, USRA, NASA Ames Research Center, Building N232, M/S 232-12, P.O. Box 1, Moffett Field, CA 94035-0001, USA
20 Department of Astrophysical Sciences, Princeton University, 4 Ivy Lane, Princeton, NJ 08544, USA
21 Centre for Astrophysics and Supercomputing, Swinburne University of Technology, John Street, Hawthorn, VIC 3122, Australia
22 Melbourne Data Analytics Platform (MDAP), The University of Melbourne, Parkville, VIC 3010, Australia

More about ASTRO 3D:

ASTRO 3D is a seven-year $40 million Centre of Excellence project funded by the Australian Government through the Australian Research Council. The Centre began in June 2017 and will end in June 2024. It hosts around 200 investigators and professional staff, mostly based at six nodes: the Australian National University, Curtin University, Swinburne University of Technology, University of Melbourne, University of Sydney, and University of Western Australia.