Completion of the 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-meter 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 fibers to capture and analyze bands of colors, 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.

The SAMI instrument inside the Anglo Australian Telescope being readied for action. Credit: ngel R. Lpez-Snchez (AAO-MQ)

No two galaxies are alike. They have different bulges, haloes, disks, and rings. Some are forming new generations of stars, while others havent 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 (February 2, 2021) 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 galaxys spin depends on the other galaxies around it, and changes depending on the galaxys 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.

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

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 weve 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 weve 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.

Reference: The SAMI Galaxy Survey: the third and final data release by Scott M Croom, Matt S Owers, Nicholas Scott, Henry Poetrodjojo, Brent Groves, Jesse van de Sande, Tania M Barone, Luca Cortese, Francesco DEugenio, Joss Bland-Hawthorn, Julia Bryant, Sree Oh, Sarah Brough, James Agostino, Sarah Casura, Barbara Catinella, Matthew Colless, Gerald Cecil, Roger L Davies, Michael J Drinkwater, Simon P Driver, Ignacio Ferreras, Caroline Foster, Amelia Fraser-McKelvie, Jon Lawrence, Sarah K Leslie, Jochen Liske, ngel R Lpez-Snchez, Nuria P F Lorente, Rebecca McElroy, Anne M Medling, Danail Obreschkow, Samuel N Richards, Rob Sharp, Sarah M Sweet, Dan S Taranu, Edward N Taylor, Edoardo Tescari, Adam D Thomas, James Tocknell and Sam P Vaughan, 1 February 2021, Monthly Notices of the Royal Astronomical Society.DOI: 10.1093/mnras/stab229

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.

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Complex Mechanics of the Evolution of the Universe: The Secrets of 3000 Galaxies Laid Bare - SciTechDaily