The evolution of galaxies is directly linked to the gas reservoirs surrounding them, known as the circumgalactic medium (CGM). The CGM is a massive multiphase gas reservoir that resides within the virial radius of their galaxies.

Simulations and observations predict that the CGM flows into galaxies along filaments from the intergalactic medium (IGM) providing fuel to form new stars. Stars lose mass as they evolve and many stars explode as supernovae and gas is ejected, feeding back into the CGM/IGM.

This feedback loop continuously shapes a galaxy’s morphology, growth and chemical make-up. Understanding the cycle of how gas is fed into and expelled out of galaxies through the CGM is critical in determining how galaxies form and evolve. 

Due to the diffuse and extended nature of the CGM and IGM, the gas cannot be observed using current imaging techniques. The CGM/IGM is only detected in spectra of bright background objects, such as pulsars, fast radio bursts, quasars, and galaxies, which are used to measure the abundance, chemical composition, kinematics, and ionisation state of gas surrounding foreground galaxies.

Given the difficulty of observing this gas, our astronomers use world-leading facilities such as the Keck Observatory, the Hubble Space Telescope, the European Southern Observatory and the Australian Square Kilometre Array Pathfinder.  We also use a range of cutting-edge cosmological simulations to interpret our observations of the CGM and IGM.

Our astronomers have used the techniques and facilities mentioned above to study the amount of gas and its relationship to their galaxies from z=0-6. We have also discovered the missing baryons in the universe and measured the size or mass of gas systems called damped Lyman alpha systems that are believed to be galaxies in formation. They explore how CGM metallicities, kinematics, galaxy orientations and environment can be used to infer the origins of the gas.

The CGM is also being used to test our understanding of physics by determining whether fundamental constants vary with location, density and time. Finally, we are pushing the observational limits by conducting direct spectral-imaging of outflows and the CGM near galaxies.

Did you know?

Our current understanding of physics may actually vary with time. Our astronomers are using the European Southern Observatory to place the world’s best constraints on how much the fundamental constants can vary with space and time.

Our projects

UVES SQUAD: The UVES Spectral Quasar Absorption Database 

UVES SQUAD is the largest set of high-resolution quasar spectra, built from the data archives of the UVES instrument on the 8-metre Very Large Telescope, and has contributed to a wide array of cosmology, quasar and circumgalactic/intergalactic medium studies so far.

Learn more

Discovering remnants of the first stars 

Within spectra of distant quasars from the world's best optical telescopes, we are discovering rare, almost pristine gas clouds that may have been enriched with the metallic debris from the explosions of the universe's first stars.

Learn more

Linking the circumgalactic medium to galaxies 

Our Multiphase Galaxy Halos Survey uses both observations and simulations to determine how the CGM influences and drives galaxy evolution.

Learn more

The physics of gas flows around galaxies at cosmic noon 

We are examining the circumgalactic medium at the universe’s epoch of peak star formation in order to address how the evolution of galaxies is influenced by gas flows.

Learn more

The nature of damped Lyman alpha systems 

Detecting damped Lyman alpha systems (DLAs) in sightlines to galaxies, as opposed to quasars done previously, is a new approach that will be used by 30m telescopes in the future able to determine the size, mass and kinematics of DLAs for the first time to understand their nature and to perform 3D neutral hydrogen tomography in the early universe.

Learn more

Understanding galaxy evolution through HI observations 

Using observations from next generation radio telescopes, this project aims to understand the fundamental physical processes affecting galaxy evolution in the local universe including angular momentum, gravitational interactions and hydrodynamical processes.

DUVET Survey 

We’re using the faintest spectral features in galaxies to make fundamental constraints on how stars form and impact the galaxy and circumgalactic medium around them.

Our astronomers use world-leading facilities such as the Keck Observatory, the Hubble Space Telescope, the European Southern Observatory and the Australian Square Kilometre Array Pathfinder.


The MeerKAT Habitat of Galaxies Survey (MeerHoGS) aims to investigate the role of environment in the baryon cycle of galaxies by combining HI interferometric imaging from the MeerKAT SKA Pathfinder with multiwavelength tracers of stellar mass and star formation.

MeerKAT will enable unprecedented studies of intragroup HI and tidal debris, particularly in group environments.

Fast radio bursts with ASKAP 

Co-led at Swinburne, the Commensal Real-time Fast Transient (CRAFT) survey detects and localises fast radio bursts with the ASKAP array to both determine what causes FRBs and use them as cosmological probes.

Learn more

Ionisation and metals 

We are investigating how Lyman-continuum photons escape from star-forming regions and into the intergalactic medium, and how metals escape galaxies, especially in the early universe. 

For more information, contact Associate Professor Emma Ryan-Weber.

Fundamental constants in distant galaxies 

Using quasars as powerful background beacons, we are searching for cosmological variations in the fundamental constants of nature by studying gas in the outskirts of distant galaxies with the world's best telescopes.

Learn more

Weighing the universe with deuterium 

This project aims to weigh the universe by comparing the amount of hydrogen and its main isotope, deuterium, in distant, almost pristine clouds of gas.

Learn more

Lyman continuum galaxies - uncovering the sources of reionisation 

This project uses the Hubble Space Telescope, Keck Telescope, and other deep imaging and spectroscopy to uncover the sources responsible for the Epoch of Reionisation (EoR) and understand their physics and mechanisms of ionising flux escape.

Learn more

Our people

See related research themes

Contact the Centre for Astrophysics and Supercomputing

If you have any questions, or are looking for more information, feel free to contact our office on +61 3 9214 8000 or at

Contact us