Overview
Background
I am a Senior Research Fellow in Cosmology based in the School of Mathematics and Physics. I work on making maps of the positions and motions of millions of galaxies in our Universe to uncover how it has evolved since the Big Bang. Current observations suggest 95% of our Universe consists of ellusive Dark Matter and Dark Energy; we can detect these by the influence they have on the light from galaxies, stars and that permeates the background Universe itself, but they don't emit light themselves and we have no idea yet what they are. My research seeks to uncover these using the largest galaxy surveys in the world.
I have been involved in planning, carrying out, and analysing a large number of these surveys. I currently working groups in the American-led Dark Energy Spectroscopic Instrument (DESI) project, the WALLABY survey based in Western Australia, and the 4MOST Hemisphere Survey (4HS) which will be carried out from Chile. Combined, these will produce the most detailed maps of galaxy positions and motions ever created --- over 40,000,000 unique galaxies!
My personal research makes use of state-of-the art computing techniques to simulate the distributions of these galaxies, their properties, and how fast they are moving. I then analyse these distributions using different statistical techniques and compare to the real data. The properties of Dark Matter and Dark Energy and all the other things that make up our Universe can then be extracted by modelling these statistics with theoretical models, or looking for discrepancies between the simulations and the data. My hope is that by doing so, we are currently on the cusp of uncovering something fundamental about how the Universe came to be the way it is today, and what will happen to it in the future.
Academic Background
- Undergraduate: MPhys 1st Class Honours - University of Sussex, 2008-2012
- Postgraduate: PhD - University of Portmouth, 2012-2016
- Research Associate - University of Western Australia, 2015-2019
- Research Fellow in Cosmology - University of Queensland, 2019-
Availability
- Dr Cullan Howlett is:
- Not available for supervision
- Media expert
Fields of research
Qualifications
- Doctor of Philosophy, University of Portsmouth
Research interests
-
Testing gravity using galaxy positions and motions
One compelling way to explain dark matter and dark energy is that our current theory of gravity (General Relativity) doesn't work on scales much larger than the Solar system. One of my interests is developing different models and understanding how they can be proven or disproven with galaxy properties.
-
Fast simulations of large scale structure
Current state of the art simulations are able to simulate the distributions of billions of galaxies, but these are very slow and can take weeks to run on the largest supercomputers. I'm interested in new approximate ways for generating these simulations or cool computational techniques such as machine learning, that can be run in a fraction of the time, or on fewer processors.
-
New statistical methods for analysing distributions of galaxies
In addition to theoretical developments, I'm interested in looking for new statistical ways to use the galaxy data we have to give us insight into the Universe.
-
Gravitational waves
Gravitational waves, first detected in 2015 are the new hot topic in physics and offer interesting ways to test cosmology. I'm interested in creating simulated catalogues of gravitational waves and using these to working out what cosmological insights gravitational waves can bring
Research impacts
The nature of dark matter and dark energy is the biggest question in modern science. Are they particles we haven't discovered yet, or perhaps a misunderstanding of our fundamental pillars of physics (Einstein's theory of General Relativity or Quantum Mechanics). We don't know, but the answer is out there, and it's likely profound. It will change everything we know about physics, and with this understanding could come unimagined new ideas and technologies. In the same way that our modern understanding of the atom and electromagnetism has lead to the technologic marvels we have today that would seem wonderous to someone 200 years ago, in 200 years from now who knows where an understanding of the Dark parts of our Universe will take us.
In order to unlock this information, cosmologists including myself have to come up with new techniques for supercomputing, for dealing with big data problems, and for mining every possible piece of data from the surveys we have. The statistics, methods and codes we develop are cutting edge and can often be used in fields outside astronomy (for instance in finance, environmental science, business planning, and even tackling pandemics...)
Works
Search Professor Cullan Howlett’s works on UQ eSpace
2025
Journal Article
Modified gravity constraints from the full shape modeling of clustering measurements from DESI 2024
Ishak, M., Pan, J., Calderon, R., Lodha, K., Valogiannis, G., Aviles, A., Niz, G., Yi, L., Zheng, C., Garcia-Quintero, C., de Mattia, A., Medina-Varela, L., Cervantes-Cota, J.L., Andrade, U., Huterer, D., Noriega, H.E., Zhao, G., Shafieloo, A., Fang, W., Ahlen, S., Bianchi, D., Brooks, D., Burtin, E., Chaussidon, E., Claybaugh, T., Cole, S., de la Macorra, A., Dey, A., Fanning, K. ... Zou, H. (2025). Modified gravity constraints from the full shape modeling of clustering measurements from DESI 2024. Journal of Cosmology and Astroparticle Physics, 2025 (09) 053, 053-9. doi: 10.1088/1475-7516/2025/09/053
2025
Journal Article
DESI 2024 II: sample definitions, characteristics, and two-point clustering statistics
Adame, A.G., Aguilar, J., Ahlen, S., Alam, S., Alexander, D.M., Alvarez, M., Alves, O., Anand, A., Andrade, U., Armengaud, E., Avila, S., Aviles, A., Awan, H., Bailey, S., Baltay, C., Bault, A., Behera, J., BenZvi, S., Beutler, F., Bianchi, D., Blake, C., Blum, R., Brieden, S., Brodzeller, A., Brooks, D., Brown, Z., Buckley-Geer, E., Burtin, E., Calderon, R. ... The DESI collaboration (2025). DESI 2024 II: sample definitions, characteristics, and two-point clustering statistics. Journal of Cosmology and Astroparticle Physics, 2025 (7) 017, 1-85. doi: 10.1088/1475-7516/2025/07/017
2025
Journal Article
Mitigating imaging systematics for DESI 2024 emission Line Galaxies and beyond
Rosado-Marín, A.J., Ross, A.J., Seo, H., Rezaie, M., Kong, H., de Mattia, A., Zhou, R., Aguilar, J., Ahlen, S., Alves, O., Bianchi, D., Brooks, D., Burtin, E., Chaussidon, E., Chen, X., Claybaugh, T., Dawson, K.S., de la Macorra, A., Dey, A., Doel, P., Fanning, K., Ferraro, S., Forero-Romero, J.E., Gaztañaga, E., Gontcho, S.Gontcho A., Gutierrez, G., Hahn, C., Hanif, M.M.S., Howlett, C. ... Zou, H. (2025). Mitigating imaging systematics for DESI 2024 emission Line Galaxies and beyond. Journal of Cosmology and Astroparticle Physics, 2025 (07) 018, 1-46. doi: 10.1088/1475-7516/2025/07/018
2025
Journal Article
Window convolution of the galaxy clustering bispectrum
Wang, M.S., Beutler, F., Aguilar, J., Ahlen, S., Bianchi, D., Brooks, D., Claybaugh, T., de la Macorra, A., Doel, P., Font-Ribera, A., Gaztañaga, E., Gutierrez, G., Honscheid, K., Howlett, C., Kirkby, D., Lambert, A., Landriau, M., Miquel, R., Niz, G., Prada, F., Pérez-Ràfols, I., Rossi, G., Sanchez, E., Schlegel, D., Schubnell, M., Sprayberry, D., Tarlé, G. and Weaver, B.A. (2025). Window convolution of the galaxy clustering bispectrum. Journal of Cosmology and Astroparticle Physics, 2025 (06) 031, 6. doi: 10.1088/1475-7516/2025/06/031
2025
Journal Article
Constraining primordial non-Gaussianity with DESI 2024 LRG and QSO samples
Chaussidon, E., Yèche, C., de Mattia, A., Payerne, C., McDonald, P., Ross, A.J., Ahlen, S., Bianchi, D., Brooks, D., Burtin, E., Claybaugh, T., de la Macorra, A., Doel, P., Ferraro, S., Font-Ribera, A., Forero-Romero, J.E., Gaztañaga, E., Gil-Marín, H., Gontcho, S.Gontcho A., Gutierrez, G., Guy, J., Honscheid, K., Howlett, C., Huterer, D., Kehoe, R., Kirkby, D., Kisner, T., Kremin, A., Le Guillou, L. ... Zou, H. (2025). Constraining primordial non-Gaussianity with DESI 2024 LRG and QSO samples. Journal of Cosmology and Astroparticle Physics, 2025 (06) 029. doi: 10.1088/1475-7516/2025/06/029
2025
Journal Article
A sound horizon-free measurement of H0 in DESI 2024
Zaborowski, E.A., Taylor, P., Honscheid, K., Cuceu, A., de Mattia, A., Huterer, D., Krolewski, A., Martini, P., Ross, A.J., To, C., Torres, A., Ahlen, S., Bianchi, D., Brooks, D., Buckley-Geer, E., Burtin, E., Claybaugh, T., Cole, S., de la Macorra, A., Dey, Arjun, Dey, Biprateep, Doel, P., Ferraro, S., Font-Ribera, A., Forero-Romero, J.E., Gaztañaga, E., Gil-Marín, H., Gutierrez, G., Guy, J. ... Wechsler, R.H. (2025). A sound horizon-free measurement of H0 in DESI 2024. Journal of Cosmology and Astroparticle Physics, 2025 (06) 020. doi: 10.1088/1475-7516/2025/06/020
2025
Journal Article
Full-Shape analysis of the power spectrum and bispectrum of DESI DR1 LRG and QSO samples
Novell-Masot, S., Gil-Marín, H., Verde, L., Aguilar, J., Ahlen, S., Bailey, S., BenZvi, S., Bianchi, D., Brooks, D., Buckley-Geer, E., Carnero Rosell, A., Chaussidon, E., Claybaugh, T., Cole, S., Cuceu, A., Dawson, K.S., de la Macorra, A., Demina, R., Dey, A., Dey, B., Doel, P., Ferraro, S., Font-Ribera, A., Forero-Romero, J.E., Gaztañaga, E., Gontcho, S.Gontcho A., Gonzalez-Morales, A.X., Gutierrez, G., Herrera-Alcantar, H.K. ... Zou, H. (2025). Full-Shape analysis of the power spectrum and bispectrum of DESI DR1 LRG and QSO samples. Journal of Cosmology and Astroparticle Physics, 2025 (06) 005. doi: 10.1088/1475-7516/2025/06/005
2025
Journal Article
Cosmological constraints from the cross-correlation of DESI Luminous Red Galaxies with CMB lensing from Planck PR4 and ACT DR6
Sailer, Noah, Kim, Joshua, Ferraro, Simone, Madhavacheril, Mathew S., White, Martin, Abril-Cabezas, Irene, Aguilar, Jessica Nicole, Ahlen, Steven, Richard Bond, J., Brooks, David, Burtin, Etienne, Calabrese, Erminia, Chen, Shi-Fan, Choi, Steve K., Claybaugh, Todd, Dawson, Kyle, de la Macorra, Axel, DeRose, Joseph, Dey, Arjun, Dey, Biprateep, Doel, Peter, Dunkley, Jo, Embil-Villagra, Carmen, Farren, Gerrit S., Font-Ribera, Andreu, Forero-Romero, Jaime E., Gaztañaga, Enrique, Gluscevic, Vera, Gontcho, Satya Gontcho A. ... Zou, Hu (2025). Cosmological constraints from the cross-correlation of DESI Luminous Red Galaxies with CMB lensing from Planck PR4 and ACT DR6. Journal of Cosmology and Astroparticle Physics, 2025 (06) 008, 008-6. doi: 10.1088/1475-7516/2025/06/008
2025
Journal Article
Constraints on primordial non-Gaussianity from the cross-correlation of DESI luminous red galaxies and <i>Planck</i> CMB lensing
Bermejo-Climent, J. R., Demina, R., Krolewski, A., Chaussidon, E., Rezaie, M., Ahlen, S., Bailey, S., Bianchi, D., Brooks, D., Burtin, E., Claybaugh, T., de la Macorra, A., Dey, A., Doel, P., Farren, G., Ferraro, S., Forero-Romero, J. E., Gaztañaga, E., Gontcho A Gontcho, S., Gutierrez, G., Hahn, C., Honscheid, K., Howlett, C., Kehoe, R., Kirkby, D., Kisner, T., Landriau, M., Le Guillou, L., Levi, M. E. ... Zarrouk, P. (2025). Constraints on primordial non-Gaussianity from the cross-correlation of DESI luminous red galaxies and Planck CMB lensing. Astronomy & Astrophysics, 698 A177, A177. doi: 10.1051/0004-6361/202453446
2025
Journal Article
Atacama Cosmology Telescope DR6 and DESI: Structure growth measurements from the cross-correlation of DESI legacy imaging galaxies and CMB lensing from ACT DR6 and Planck PR4
Qu, Frank J., Hang, Qianjun, Farren, Gerrit, Bolliet, Boris, Aguilar, Jessica Nicole, Ahlen, Steven, Alam, Shadab, Brooks, David, Cai, Yan-Chuan, Calabrese, Erminia, Claybaugh, Todd, De La MacOrra, Axel, Devlin, Mark J., Doel, Peter, Embil-Villagra, Carmen, Ferraro, Simone, Font-Ribera, Andreu, Forero-Romero, Jaime E., Gaztañaga, Enrique, Gluscevic, Vera, Gontcho, Satya Gontcho A., Gutierrez, Gaston, Howlett, Cullan, Kehoe, Robert, Kim, Joshua, Kremin, Anthony, Lambert, Andrew, Landriau, Martin, Le Guillou, Laurent ... Zou, Hu (2025). Atacama Cosmology Telescope DR6 and DESI: Structure growth measurements from the cross-correlation of DESI legacy imaging galaxies and CMB lensing from ACT DR6 and Planck PR4. Physical Review D, 111 (10) 103503. doi: 10.1103/PhysRevD.111.103503
2025
Journal Article
DESI Peculiar Velocity Survey – Fundamental Plane
Said, Khaled, Howlett, Cullan, Davis, Tamara, Lucey, John, Saulder, Christoph, Douglass, Kelly, Kim, Alex G, Kremin, Anthony, Ross, Caitlin, Aldering, Greg, Aguilar, Jessica Nicole, Ahlen, Steven, BenZvi, Segev, Bianchi, Davide, Brooks, David, Claybaugh, Todd, Dawson, Kyle, de la Macorra, Axel, Dey, Biprateep, Doel, Peter, Fanning, Kevin, Ferraro, Simone, Font-Ribera, Andreu, Forero-Romero, Jaime E, Gaztañaga, Enrique, Gontcho, Satya Gontcho A, Guy, Julien, Honscheid, Klaus, Kehoe, Robert ... Zou, Hu (2025). DESI Peculiar Velocity Survey – Fundamental Plane. Monthly Notices of the Royal Astronomical Society, 539 (4), 3627-3644. doi: 10.1093/mnras/staf700
2025
Journal Article
Analytical and EZmock covariance validation for the DESI 2024 results
Forero-Sánchez, D., Rashkovetskyi, M., Alves, O., de Mattia, A., Padmanabhan, N., Seo, H., Nadathur, S., Ross, A.J., Gil-Marín, H., Zarrouk, P., Yu, J., Ding, Z., Andrade, U., Chen, X., Garcia-Quintero, C., Mena-Fernández, J., Ahlen, S., Bianchi, D., Brooks, D., Burtin, E., Chaussidon, E., Claybaugh, T., Cole, S., de la Macorra, A., Enriquez-Vargas, M., Gaztañaga, E., Gutierrez, G., Honscheid, K., Howlett, C. ... Zou, H. (2025). Analytical and EZmock covariance validation for the DESI 2024 results. Journal of Cosmology and Astroparticle Physics, 2025 (04) 055, 055. doi: 10.1088/1475-7516/2025/04/055
2025
Journal Article
DESI 2024 III: baryon acoustic oscillations from galaxies and quasars
Adame, A.G., Aguilar, J., Ahlen, S., Alam, S., Alexander, D.M., Alvarez, M., Alves, O., Anand, A., Andrade, U., Armengaud, E., Avila, S., Aviles, A., Awan, H., Bailey, S., Baltay, C., Bault, A., Behera, J., BenZvi, S., Beutler, F., Bianchi, D., Blake, C., Blum, R., Brieden, S., Brodzeller, A., Brooks, D., Buckley-Geer, E., Burtin, E., Calderon, R., Canning, R. ... The DESI collaboration (2025). DESI 2024 III: baryon acoustic oscillations from galaxies and quasars. Journal of Cosmology and Astroparticle Physics, 2025 (4) 012, 1-72. doi: 10.1088/1475-7516/2025/04/012
2025
Journal Article
Characterization of DESI fiber assignment incompleteness effect on 2-point clustering and mitigation methods for DR1 analysis
Bianchi, D., Hanif, M.M.S., Carnero Rosell, A., Lasker, J., Ross, A.J., Pinon, M., de Mattia, A., White, M., Ahlen, S., Bailey, S., Brooks, D., Burtin, E., Chaussidon, E., Claybaugh, T., Cole, S., de la Macorra, A., Ferraro, S., Font-Ribera, A., Forero-Romero, J.E., Gaztañaga, E., Gontcho, S.Gontcho A., Gutierrez, G., Guy, J., Hahn, C., Honscheid, K., Howlett, C., Juneau, S., Kirkby, D., Kisner, T. ... Zou, H. (2025). Characterization of DESI fiber assignment incompleteness effect on 2-point clustering and mitigation methods for DR1 analysis. Journal of Cosmology and Astroparticle Physics, 2025 (04) 074, 074-4. doi: 10.1088/1475-7516/2025/04/074
2025
Journal Article
DESIVAST: Catalogs of Low-redshift Voids Using Data from the DESI Data Release 1 Bright Galaxy Survey
Rincon, Hernan, Benzvi, Segev, Douglass, Kelly, Veyrat, Dahlia, Aguilar, Jessica Nicole, Ahlen, Steven, Bianchi, Davide, Brooks, David, Claybaugh, Todd, Cole, Shaun, de la Macorra, Axel, Doel, Peter, Font-Ribera, Andreu, Forero-Romero, Jaime E., Gaztañaga, Enrique, Gontcho A Gontcho, Satya, Gutierrez, Gaston, Honscheid, Klaus, Howlett, Cullan, Juneau, Stephanie, Kehoe, Robert, Koposov, Sergey, Lambert, Andrew, Landriau, Martin, Le Guillou, Laurent, Meisner, Aaron, Miquel, Ramon, Moustakas, John, Niz, Gustavo ... Zou, Hu (2025). DESIVAST: Catalogs of Low-redshift Voids Using Data from the DESI Data Release 1 Bright Galaxy Survey. The Astrophysical Journal, 982 (1) 38, 38-1. doi: 10.3847/1538-4357/adb559
2025
Journal Article
Constraining the phase shift of relativistic species in DESI BAOs
Whitford, Abbé M, Rivera-Morales, Hugo, Howlett, Cullan, Vargas-Magaña, Mariana, Fromenteau, Sébastien, Davis, Tamara M., Pérez-Fernández, Alejandro, de Mattia, Arnaud, Ahlen, Steven, Bianchi, Davide, Brooks, David, Burtin, Etienne, Claybaugh, Todd, de la Macorra, Axel, Doel, Peter, Ferraro, Simone, Forero-Romero, Jaime E, Gaztañaga, Enrique, Gontcho, Satya Gontcho A, Gutierrez, Gaston, Juneau, Stephanie, Kehoe, Robert, Kirkby, David, Kisner, Theodore, Koposov, Sergey, Landriau, Martin, Le Guillou, Laurent, Meisner, Aaron, Miquel, Ramon ... Zou, Hu (2025). Constraining the phase shift of relativistic species in DESI BAOs. Monthly Notices of the Royal Astronomical Society, 538 (3), 1980-2000. doi: 10.1093/mnras/staf394
2025
Journal Article
Candidate strongly lensed type Ia supernovae in the Zwicky Transient Facility archive
Townsend, Alice, Nordin, Jakob, Sagués Carracedo, Ana, Kowalski, Marek P., Arendse, Nikki, Dhawan, Suhail, Goobar, Ariel M., Johansson, Joel P., Mörtsell, Edvard, Schulze, Steve, Andreoni, Igor, Fernández, E., Kim, Alex G., Nugent, Peter E., Prada, F., Rigault, M., Sarin, N., Sharma, D., Bellm, E. C., Coughlin, M. W., Dekany, R., Groom, S. L., Lacroix, L., Laher, R. R., Riddle, R., Aguilar, J., Ahlen, S., Bailey, S., Brooks, D. ... Zou, H. (2025). Candidate strongly lensed type Ia supernovae in the Zwicky Transient Facility archive. Astronomy and Astrophysics, 694 A146. doi: 10.1051/0004-6361/202451082
2025
Journal Article
DESI 2024 VI: cosmological constraints from the measurements of baryon acoustic oscillations
Adame, A.G., Aguilar, J., Ahlen, S., Alam, S., Alexander, D.M., Alvarez, M., Alves, O., Anand, A., Andrade, U., Armengaud, E., Avila, S., Aviles, A., Awan, H., Bahr-Kalus, B., Bailey, S., Baltay, C., Bault, A., Behera, J., BenZvi, S., Bera, A., Beutler, F., Bianchi, D., Blake, C., Blum, R., Brieden, S., Brodzeller, A., Brooks, D., Buckley-Geer, E., Burtin, E. ... The DESI collaboration (2025). DESI 2024 VI: cosmological constraints from the measurements of baryon acoustic oscillations. Journal of Cosmology and Astroparticle Physics, 2025 (02) 021, 1-70. doi: 10.1088/1475-7516/2025/02/021
2025
Journal Article
Improving the determination of supernova cosmological redshifts by using galaxy groups
Peterson, Erik R., Carreres, Bastien, Carr, Anthony, Scolnic, Daniel, Bailey, Ava, Davis, Tamara M., Brout, Dillon, Howlett, Cullan, Jones, David O., Riess, Adam G., Said, Khaled and Taylor, Georgie (2025). Improving the determination of supernova cosmological redshifts by using galaxy groups. The Astrophysical Journal, 980 (1) 21, 1-14. doi: 10.3847/1538-4357/ada285
2025
Journal Article
Full Modeling and parameter compression methods in configuration space for DESI 2024 and beyond
Ramirez-Solano, S., Icaza-Lizaola, M., Noriega, H.E., Vargas-Magaña, M., Fromenteau, S., Aviles, A., Rodríguez-Martínez, F., Aguilar, J., Ahlen, S., Alves, O., Brieden, S., Brooks, D., Claybaugh, T., Cole, S., de la Macorra, A., Dey, Arjun, Dey, B., Doel, P., Fanning, K., Forero-Romero, J.E., Gaztañaga, E., Gil-Marín, H., Gontcho, S.Gontcho A., Honscheid, K., Howlett, C., Juneau, S., Lai, Y., Landriau, M., Manera, M. ... Zou, H. (2025). Full Modeling and parameter compression methods in configuration space for DESI 2024 and beyond. Journal of Cosmology and Astroparticle Physics, 2025 (1) 129. doi: 10.1088/1475-7516/2025/01/129
Funding
Current funding
Supervision
Availability
- Dr Cullan Howlett is:
- Not available for supervision
Supervision history
Current supervision
-
Doctor Philosophy
Fundamental Plane distances from the Dark Energy Spectroscopic Instrument
Principal Advisor
Other advisors: Professor Tamara Davis
-
Doctor Philosophy
Direct detection of dark matter and exotic physics through atomic systems
Associate Advisor
Other advisors: Associate Professor Jacinda Ginges, Dr Benjamin Roberts
-
Doctor Philosophy
Cosmological Constraints with large-scale structure: from LambdaCDM to light relics
Associate Advisor
Other advisors: Professor Tamara Davis
-
Doctor Philosophy
Gravitational wave cosmology
Associate Advisor
Other advisors: Professor Tamara Davis
-
Doctor Philosophy
Cosmology with the Dark Energy Survey
Associate Advisor
Other advisors: Professor Tamara Davis
Completed supervision
-
2025
Doctor Philosophy
Using the motions of galaxies to probe fundamental physics
Principal Advisor
Other advisors: Professor Tamara Davis
-
2025
Doctor Philosophy
Completing the Puzzle: Unveiling Clues for Gravitational Wave Astrophysics and Cosmology with Simulations
Principal Advisor
Other advisors: Professor Tamara Davis
-
2023
Doctor Philosophy
Whispers from the Big Bang-Cosmological Constraints from Galaxy Power Spectra
Principal Advisor
Other advisors: Professor Tamara Davis
Media
Enquiries
Contact Dr Cullan Howlett directly for media enquiries about:
- Astronomy
- Astrophysics
- Cosmology
- Dark energy
- Dark matter
Need help?
For help with finding experts, story ideas and media enquiries, contact our Media team: