Dr Cullan Howlett

I am a cosmologist working on using the properties of the large scale distribution of galaxies to try and understand our Universe: what it’s made of, how it came to be today, and what will happen to it in the future. For decades now, we have known that our current model of the Universe is lacking, and we are unable to explain many of the observation we have made of the properties of galaxies both in our Local Group and on larger scales. Possible solutions to this include adding in exotic components such as Dark Matter and Dark Energy to the make-up of our Universe: components that (as far as we know!) don’t emit any light but can be felt by their gravitational influence on the cosmos. Another possibility is that our current theory of gravity, Einstein’s General Relativity, does not work on scales outside our solar neighbourhood.

Measurements of the 3D distribution of galaxies can be used to test gravity and help us understand the nature of the dark ‘sector’ of our Universe. There is a huge amount of information encoded in this. Two of the main measurements I’m interested in are:

• The Baryon Acoustic Oscillation feature in the clustering of galaxies, which is the remnants of sound waves that travelled through baryonic plasma in the hot, early universe. These sound waves have a characteristic size, and so by measuring their size at different points in the past, we can work out how our Universe has expanded and evolved over time.
• Galaxy peculiar velocities and Redshift Space Distortions. Galaxies are drawn towards high density regions of the universe under the influence of gravity, this gives the galaxies some velocity relative to us. In some cases this can be measured directly, and in general it creates Redshift Space Distortions in the galaxy positions when averaged over large numbers of galaxies. Measuring either of these can provide a strong test of our gravitational theories.

Obtaining such measurements requires large numbers of galaxy observations, which requires large teams of scientists working together at some of the best telescopes in the world. I am currently involved in analysing the 2MASS Tully-Fisher survey (Click HERE for some material on this) and am Co-Chair of the cosmology working group for the Taipan Galaxy Survey. In the past I have also worked with the Sloan Digital Sky Survey Main Galaxy Sample and Baryon Oscillation Spectroscopic Survey.

On top of this, understanding these observations requires complex models, and large numbers of simulations run on supercomputers. To that end, I have developed very fast, MPI-parallel codes for generating dark matter simulations (L-PICOLA) and converting those simulations to dark matter halos (CM_Halofinder). Both of these can be found on my GitHub page. For any one interested, a full list of my refereed publications can be found HERE, whilst a (outdated!) copy of my CV can be found HERE.

On top of my research interests, I am also a strong believer in fairness, equity and diversity in the workplace. I am a member of ICRAR’s Diversity, Equity and Inclusivity commitee and am in charge of organising the mentoring scheme for ICRAR/UWA PhD students/postdocs. I am Dark theme scientist for CAASTRO and a member of the CAASTRO Postdoc Commitee.