Professor Stuart Wyithe

BSc (Hons), PhD, The University of Melbourne
Director, Research School of Astronomy and Astrophysics
ANU College of Science

Areas of expertise

  • Cosmology And Extragalactic Astronomy 510103

Research interests

The quest to try and understand how the Universe came to look the way it does lies at the heart of astronomy. However when viewing the Universe from a historical perspective astronomers are immediately faced with fundamental unanswered questions. We believe the Universe has a finite age, and as a result, that there must have been an epoch when galaxies appeared for the first time. However we do not know how this first generation of galaxies formed. We do not know what they looked like, or how big they were. Indeed, we do not even know when galaxies first played an important role in the evolution of our Universe.

Over the last decade the composition of the Universe has been determined to high accuracy. Understanding the first galaxies now represents the next great challenge for observational cosmology. Currently, our knowledge of the first galaxies is currently limited to two primary facts, which are represented in the schematic of Figure 1. Astronomers understand that our Universe began with the “Big Bang”, after which the initially very hot Universe expanded and cooled. When the Universe cooled sufficiently that the gas of protons and electrons “recombined” to form atomic hydrogen, light was able to travel freely for the first time. We observe this light today as a diffuse glow on the sky known as the Cosmic Microwave Background, which describes the state of the Universe 380,000 years after the Big Bang. Small ripples of density observed at this time grew under the influence of gravity, forming the sites of modern-day galaxies some 13.7 billion years later. Some of the atomic hydrogen in the early Universe formed stars within galaxies, but most is located in the space between galaxies. The current belief is that the first galaxies appeared a few hundred million years after the Big Bang, resulting in a large UV flux that reionised hydrogen in the Universe. The time when galaxies first became important can be defined as the instant when the combined galaxies in the Universe had produced enough ultra-violet light to reionise all of the hydrogen. Astronomers refer to this as the end of the Dark Ages of the Universe.

There are several key observational areas in which substantial progress is being made in the study of the first galaxies. The first of these are ongoing programs with an emphasis on obtaining data beyond the current redshift, or distance frontier, using new surveys and instruments. Following the success of the Hubble Space Telescope (HST), the James Webb Space Telescope (JWST) is discovering the high redshift galaxies thought to be responsible for the reionisation of the intergalactic hydrogen. The advent of 30-meter class optical/IR telescopes in the next decade, such as the Giant Magellan telescope (GMT), will open a new window on the Universe allowing spectra to be taken of the earliest forming galaxies discovered with JWST. Much emphasis is also based on experiments to measure the redshifted 21 cm radio signal, which may provide the first direct probe of the neutral hydrogen in the high redshift Universe. Radio telescopes such as the Murchison Widefield Array in Western Australia are leading efforts in this exciting new field. Ground based surveys discover high redshift quasars, thus providing valuable additional targets for studies of the intervening intergalactic hydrogen using quasar absorption spectroscopy. Finally, the Planck cosmic microwave background experiment provide tight limits on fundamental cosmological and astrophysical parameters, providing better constraints on the integrated ionisation history of the IGM. The goal of these observations is to elucidate the physical history and origin of the first galaxies, which can only be achieved within a sophisticated physical framework.

Within this context, the development of theoretical models that include detailed physics of galaxy formation and intergalactic hydrogen therefore play a key role. At the highest redshifts astronomers have only theoretical predictions to guide knowledge of the first galaxies and their interaction with intergalactic hydrogen prior to reionisation. Further developing these theoretical models and utilizing them in combination with observational data to better understand the evolution of the IGM during the Epoch of Reionisation underpin our science program.

 

Biography

Professor Stuart Wyithe is Director of the Research School of Astronomy and Astrophysics. He was awarded his PhD from The University of Melbourne in 2001, and was a Hubble Fellow at Harvard University before returning to Australia in 2002.

Professor Wyithe' s research focus is on the evolution of the earliest galaxies and how this evolution may be studied with the next generation of telescopes. He has received several awards for this work, including an Australian Laureate Fellowship, the Pawsey Medal for physics from the Australian Academy of Science, the Malcolm McIntosh Prize for Physical Scientist of the Year and the Australian Institute of Physics Boas Medal. Professor Wyithe has also played numerous leadership roles including President of the Astronomical Society of Australia and Chair of the Australian National Committee for Astronomy. In the latter role he chaired the Australian Astronomy Decadal Plan 2015-2025.

 

Researcher's projects

The Dark-ages, Reionization And Galaxy-formation Observables Numerical Simulation project (DRAGONS) combines semi-analytic modeling for galaxy formation designed to accurately represent the growth of galaxies, with a semi-numerical model for the growth and evolution of ionized structure. The goal of DRAGONS is self-consistent modelling of observations of high redshift galaxies and the structure and morphology of reionization.

 Meraxes

Meraxes is a semi-analytic galaxy formation model, specially designed for studying galaxy formation during the Epoch of Reionisation. Meraxes includes a fully temporally and spatially coupled treatment of reionisation and is built upon the Genesis N-body simulations which possesses both sufficient volume and mass resolution to study reionisation structure as well as the temporal resolution needed to resolve the galaxy and star formation physics relevant to early galaxy formation. The primary asset setting Tiamat apart from most other large simulation programs is its high density of simulation outputs at high redshift (100 from z=35 to z=5; roughly one every 10 Myrs) enabling the construction of very accurate merger trees at an epoch when galaxy formation is rapid and mergers extremely frequent. We use Tiamat to analyse the dynamical evolution of galaxies at high redshift, drawing comparisons to low-redshift results from other simulations.

 

Available student projects

 

And Then There Was Light: Hunting the First Stars in the Universe [Video]

Simulating the formation of the first galaxies.

This project will build on work within the Dark-ages, Reionization And Galaxy-formation Observables Numerical Simulation project (DRAGONS) which combines semi-analytic modeling for galaxy formation designed to accurately represent the growth of galaxies, with a semi-numerical model for the growth and evolution of ionized structure. The goal of DRAGONS is self-consistent modelling of observations of high redshift galaxies and the structure and morphology of reionization.

The James Webb Space Telescope has revolutionized our view of the formation of galaxies at the highest redshifts. Understanding how mass buids up in these galaxies and how the stars formed interact with the intergalactic and interstellar media requires detailed simulations. 

Specific projects include investigating:

1) how emission lines can be used to accurately determine star-formation rates, metalicities and escape of ionizing radiation that reionizes the IGM,

2) the origin of massive quiescent galaxies and how these can have formed at such high redshift,

3) How observations of the IGM with the Square Kilometer Array will uncover the properties of faint galaxies.  

 

Projects and Grants

Grants information is drawn from ARIES. To add or update Projects or Grants information please contact your College Research Office.

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Updated:  23 June 2024 / Responsible Officer:  Director (Research Services Division) / Page Contact:  Researchers