The Top 3
For the 2024 Annual Report, the project and survey leads were asked to provide their Top 3 science/project outcomes from the full seven and a half years of the Centre. We have used these to showcase some of the big, impactful outcomes of the Centre.
In the local Universe, ASTRO 3D made strides in solving the cosmological lithium problem, and defined chemical clocks to help reconstruct the timeline of star formation and chemical enrichment in the Milky Way.
ASTRO 3D defined 'The Avocado and Egg Plot': using chemical composition ratios such as [Na/Fe] vs. [Mg/Mn], GALAH differentiated stars formed in the Milky Way from those accreted from external galaxies. The ‘avocado’ distribution represents native stars, while ‘scrambled eggs’ denote accreted populations, offering a clear visualisation of the galaxy’s assembly history that allows us to study the important of galaxy collisions on the Milky Way's present shape. ASTRO 3D led the first detailed analysis, using theoretical nucleosynthetic yields and event rates for all chemical enrichment sources, of the build-up of the chemical elements in the solar neighbourhood from the Big Bang to the present-day.
ASTRO 3D also discovered that binary neutron star (NS) mergers are a likely source for the nucleosynthesis of rapid-neutron-capture (r-process) elements such as Eu, but because of the time delay in the formation of a NS-NS binary and its subsequent merger, binary NS mergers are unlikely to contribute to the formation of r-process elements at very low overall abundances/old ages. The result indicates that similar explosions of fast-spinning strongly magnetized stars likely occurred during the earliest epochs of star formation in our Galaxy.
In addition, asteroseismology data from the Kepler spacecraft (K2 mission) was used to accurately determine masses for red giants in globular clusters. The results are the first direct quantitative measurement of substantial numbers of masses of globular clusters stars. The results also confirm the prediction that mass-loss scales with cluster metallicity. In the radio, the WALLABY data release contains more galaxies than available from any previous interferometric survey, greatly expanding our knowledge of gas distribution and kinematics of galaxies in the local Universe.
In the low-to-mid redshift Universe, the FLASH team has published the first unbiased sample of HI absorption lines at intermediate redshift, from a pilot survey of 3,000 square degrees of sky. Nikki Nielson showed, for the first time, a direct, high-resolution map of optical emission lines from material outside of a galaxy in the circumgalactic medium.
Kate Harborne (PhD student to postdoc) was responsible for one of the most influential codes developed during this time. 'SimSpin v2.6.0—constructing synthetic spectral IFU cubes for comparison with observational surveys' is the latest version of SimSpin, which is used to generate synthetic integral field spectroscopic data cubes of simulated galaxies. This provides a crucial tool to forward model predictions for observed IFS studies of galaxies from state-of-the-art cosmological simulations.
PhD student Dian Triani developed a semi-analytic model called Dusty SAGE to study dust evolution in galaxies, incorporating detailed dust tracking mechanisms. This model successfully reproduced observed dust properties and scaling relations, revealing that grain growth dominates dust production in the local universe (z < 3), while stellar ejecta are the primary source in the early universe (z> 3).
A deeper understanding of what drives the dynamical structure of galaxies; through a series of papers the SAMI team discovered the main parameters that control galaxy spin. While mass and environment are related to spin, it appears that stellar population age is the most dominant factor. Discovery that galaxy spin aligns with large-scale structure. The SAMI team were the first to show that the direction a galaxy spins depends on its position relative to the sheets and filaments of the large-scale structure of the Universe. The team showed that low-mass galaxies have spin vectors aligned with filaments, while high-mass galaxies have their spin vectors perpendicular to filaments. This alignment seems most strongly related to the bulge mass of the galaxies. Galaxies in groups seem to quench more slowly, while the quenching does not seem to happen at the same time as changes in kinematics.
DINGO has created the deepest spectral-line (and continuum) images from ASKAP, paving the way for even longer integration imaging as the survey progresses, as well as future deep studies with the SKA.
In the high-redshift Universe, PhD student Balu Sreedhar used the Meraxes semi-analytic model with large volume N-body simulations to study the effect of X-rays from the first galaxies on the thermal evolution of the IGM, and to make predictions of the global 21cm signature of reionization in a model that includes self-consistent modelling of galaxies for the first time.
The MWA EoR team published the largest set of data for probing the intergalactic hydrogen gas in the first billion years of the Universe, and ruled out cold reionization models. ASTRO 3D also produced the deepest, widest and most complete model of the southern sky below 200MHz using the Murchison Widefield Array, providing the best calibration model for MWA and the future SKA-Low.
Boyett and team used JWST observations to identify a set of galaxies that are more massive and have kinematics and spatial properties consistent with merging galaxies, providing evidence of a rapid and efficient build-up of mass and metals in the immediate aftermath of the Big Bang through mergers.
