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
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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.
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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.
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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.
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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
Clustering of DESI galaxies split by thermal Sunyaev-Zeldovich effect
Rashkovetskyi, Michael, Eisenstein, Daniel J., Aguilar, Jessica Nicole, Ahlen, Steven, Anand, Abhijeet, Bianchi, Davide, Brooks, David, Castander, Francisco Javier, Claybaugh, Todd, Cuceu, Andrei, Dawson, Kyle S., de la Macorra, Axel, Dey, Arjun, Doel, Peter, Ferraro, Simone, Font-Ribera, Andreu, Forero-Romero, Jaime E., Gaztañaga, Enrique, Gutierrez, Gaston, Herrera-Alcantar, Hiram K., Honscheid, Klaus, Howlett, Cullan, Ishak, Mustapha, Joyce, Richard, Kehoe, Robert, Kisner, Theodore, Kremin, Anthony, Lahav, Ofer, Lambert, Andrew ... Zou, Hu (2025). Clustering of DESI galaxies split by thermal Sunyaev-Zeldovich effect. The Open Journal of Astrophysics, 8. doi: 10.33232/001c.146033
2025
Journal Article
Cosmological implications of DESI DR2 BAO measurements in light of the latest ACT DR6 CMB data
Garcia-Quintero, C., Noriega, H. E., de Mattia, A., Aviles, A., Lodha, K., Chebat, D., Rohlf, J., Nadathur, S., Elbers, W., Aguilar, J., Ahlen, S., Alves, O., Andrade, U., Bailey, S., BenZvi, S., Bianchi, D., Brooks, D., Burtin, E., Calderon, R., Carnero Rosell, A., Carrilho, P., Castander, F. J., Chaussidon, E., Claybaugh, T., Cole, S., Cuceu, A., de Belsunce, R., de la Macorra, A., Deiosso, N. ... Zhou, R. (2025). Cosmological implications of DESI DR2 BAO measurements in light of the latest ACT DR6 CMB data. Physical Review D, 112 (8) 083529. doi: 10.1103/d6yc-xpqb
2025
Journal Article
Author Correction: Dynamical dark energy in light of the DESI DR2 baryonic acoustic oscillations measurements
Gu, Gan, Wang, Xiaoma, Wang, Yuting, Zhao, Gong-Bo, Pogosian, Levon, Koyama, Kazuya, Peacock, John A., Cai, Zheng, Cervantes-Cota, Jorge L., Ishak, Mustapha, Shafieloo, Arman, Zhao, Ruiyang, Ahlen, Steven, Bianchi, Davide, Brooks, David, Claybaugh, Todd, Cole, Shaun, de la Macorra, Axel, de Mattia, Arnaud, Doel, Peter, Ferraro, Simone, Forero-Romero, Jaime E., Gaztañaga, Enrique, Gontcho A Gontcho, Satya, Gutierrez, Gaston, Hahn, ChangHoon, Howlett, Cullan, Kehoe, Robert, Kirkby, David ... Zou, Hu (2025). Author Correction: Dynamical dark energy in light of the DESI DR2 baryonic acoustic oscillations measurements. Nature Astronomy, 9 (12), 1898-1898. doi: 10.1038/s41550-025-02698-1
2025
Journal Article
Extended dark energy analysis using DESI DR2 BAO measurements
Lodha, K., Calderon, R., Matthewson, W. L., Shafieloo, A., Ishak, M., Pan, J., Garcia-Quintero, C., Huterer, D., Valogiannis, G., Ureña-López, L. A., Kamble, N. V., Parkinson, D., Kim, A. G., Zhao, G. B., Cervantes-Cota, J. L., Rohlf, J., Lozano-Rodríguez, F., Román-Herrera, J. O., Abdul-Karim, M., Aguilar, J., Ahlen, S., Alves, O., Andrade, U., Armengaud, E., Aviles, A., Behera, J., BenZvi, S., Bianchi, D., Brodzeller, A. ... DESI Collaboration (2025). Extended dark energy analysis using DESI DR2 BAO measurements. Physical Review D, 112 (8) 083511. doi: 10.1103/w4c6-1r5j
2025
Journal Article
Validation of the DESI DR2 measurements of baryon acoustic oscillations from galaxies and quasars
Andrade, U., Paillas, E., Mena-Fernández, J., Li, Q., Ross, A. J., Nadathur, S., Rashkovetskyi, M., Pérez-Fernández, A., Seo, H., Sanders, N., Alves, O., Chen, X., Deiosso, N., de Mattia, A., White, M., Karim, M. Abdul, Ahlen, S., Armengaud, E., Aviles, A., Bansal, P., Behera, J., Bianchi, D., Brieden, S., Brodzeller, A., Brooks, D., Burtin, E., Calderon, R., Canning, R., Rosell, A. Carnero ... DESI Collaboration (2025). Validation of the DESI DR2 measurements of baryon acoustic oscillations from galaxies and quasars. Physical Review D, 112 (8) 083512, 1-41. doi: 10.1103/kdys-w8vl
2025
Journal Article
Constraints on neutrino physics from DESI DR2 BAO and DR1 full shape
Elbers, W., Aviles, A., Noriega, H. E., Chebat, D., Menegas, A., Frenk, C. S., Garcia-Quintero, C., Gonzalez, D., Ishak, M., Lahav, O., Naidoo, K., Niz, G., Yeche, C., Abdul-Karim, M., Ahlen, S., Alves, O., Andrade, U., Armengaud, E., Behera, J., Benzvi, S., Bianchi, D., Brieden, S., Brodzeller, A., Brooks, D., Burtin, E., Calderon, R., Canning, R., Rosell, A. Carnero, Casas, L. ... DESI Collaboration, (2025). Constraints on neutrino physics from DESI DR2 BAO and DR1 full shape. Physical Review D, 112 (8) 083513. doi: 10.1103/w9pk-xsk7
2025
Journal Article
DESI DR2 results. II. Measurements of baryon acoustic oscillations and cosmological constraints
Abdul Karim, M., Aguilar, J., Ahlen, S., Alam, S., Allen, L., Prieto, C. Allende, Alves, O., Anand, A., Andrade, U., Armengaud, E., Aviles, A., Bailey, S., Baltay, C., Bansal, P., Bault, A., Behera, J., BenZvi, S., Bianchi, D., Blake, C., Brieden, S., Brodzeller, A., Brooks, D., Buckley-Geer, E., Burtin, E., Calderon, R., Canning, R., Rosell, A. Carnero, Carrilho, P., Casas, L. ... DESI Collaboration (2025). DESI DR2 results. II. Measurements of baryon acoustic oscillations and cosmological constraints. Physical Review D, 112 (8) 083515, 083515-1-083515-40. doi: 10.1103/tr6y-kpc6
2025
Journal Article
DESI DR2 results. I. Baryon acoustic oscillations from the Lyman alpha forest
Abdul Karim, M., Aguilar, J., Ahlen, S., Allende Prieto, C., Alves, O., Anand, A., Andrade, U., Armengaud, E., Aviles, A., Bailey, S., Bault, A., Behera, J., BenZvi, S., Bianchi, D., Blake, C., Brodzeller, A., Brooks, D., Buckley-Geer, E., Burtin, E., Calderon, R., Canning, R., Carnero Rosell, A., Carrilho, P., Casas, L., Castander, F. J., Cereskaite, R., Charles, M., Chaussidon, E., Chaves-Montero, J. ... DESI Collaboration (2025). DESI DR2 results. I. Baryon acoustic oscillations from the Lyman alpha forest. Physical Review D, 112 (8) 083514, 1-28. doi: 10.1103/2wwn-xjm5
2025
Journal Article
Construction of the damped <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi>Ly</mml:mi><mml:mi>α</mml:mi></mml:mrow></mml:math> absorber catalog for DESI DR2 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mrow><mml:mrow><mml:mi>Ly</mml:mi><mml:mi>α</mml:mi></mml:mrow></mml:mrow></mml:mrow></mml:math> BAO
Brodzeller, A., Wolfson, M., Santos, D. M., Ho, M., Tan, T., Pieri, M. M., Cuceu, A., Abdul-Karim, M., Aguilar, J., Ahlen, S., Anand, A., Andrade, U., Armengaud, E., Aviles, A., Bailey, S., Bault, A., Bianchi, D., Brooks, D., Canning, R., Casas, L., Charles, M., Chaussidon, E., Chaves-Montero, J., Chebat, D., Claybaugh, T., Dawson, K. S., de Belsunce, R., de la Macorra, A., de Mattia, A. ... DESI Collaboration (2025). Construction of the damped Lyα absorber catalog for DESI DR2 Lyα BAO. Physical Review D, 112 (8) 083510. doi: 10.1103/wxyv-46kb
2025
Journal Article
Can a multi-tracer approach improve the constraints on the turnover scale at low redshift?
Lai, Y., Howlett, C. and Davis, T.M. (2025). Can a multi-tracer approach improve the constraints on the turnover scale at low redshift?. Journal of Cosmology and Astroparticle Physics, 2025 (10) 071, 1-39. doi: 10.1088/1475-7516/2025/10/071
2025
Journal Article
Dynamical dark energy in light of the DESI DR2 baryonic acoustic oscillations measurements
Gu, Gan, Wang, Xiaoma, Wang, Yuting, Zhao, Gong-Bo, Pogosian, Levon, Koyama, Kazuya, Peacock, John A., Cai, Zheng, Cervantes-Cot, Jorge L., Ishak, Mustapha, Shafieloo, Arman, Zhao, Ruiyang, Ahlen, Steven, Bianchi, Davide, Brooks, David, Claybaugh, Todd, Cole, Shaun, de la Macorra, Axel, de Mattia, Arnaud, Doel, Peter, Ferraro, Simone, Forero-Romero, Jaime E., Gaztañaga, Enrique, Gontcho A Gontch, Satya, Gutierrez, Gaston, Hahn, ChangHoon, Howlett, Cullan, Kehoe, Robert, Kirkby, David ... Zou, Hu (2025). Dynamical dark energy in light of the DESI DR2 baryonic acoustic oscillations measurements. Nature Astronomy, 9 (12), 1879-1889. doi: 10.1038/s41550-025-02669-6
2025
Journal Article
STag. II. Classification of serendipitous supernovae observed by galaxy redshift surveys
Davison, W., Parkinson, D., BenZvi, S., Palmese, A., Aguilar, J., Ahlen, S., Brooks, D., Claybaugh, T., de la Macorra, A., Dey, Arjun, Doel, P., Gaztañaga, E., Gontcho A Gontcho, S., Howlett, C., Juneau, S., Kisner, T., Kremin, A., Lambert, A., Landriau, M., Le Guillou, L., Meisner, A., Miquel, R., Moustakas, J., Myers, A. D., Poppett, C., Prada, F., Rezaie, M., Rossi, G., Sanchez, E. ... Zou, H. (2025). STag. II. Classification of serendipitous supernovae observed by galaxy redshift surveys. Publications of the Astronomical Society of the Pacific, 137 (9) 094001, 1-18. doi: 10.1088/1538-3873/ae015d
2025
Journal Article
Exploring HOD-dependent systematics for the DESI 2024 Full-Shape galaxy clustering analysis
Findlay, N., Nadathur, S., Percival, W.J., de Mattia, A., Zarrouk, P., Gil-Marín, H., Alves, O., Mena-Fernández, J., Garcia-Quintero, C., Rocher, A., Ahlen, S., Bianchi, D., Brooks, D., Claybaugh, T., Cole, S., de la Macorra, A., Dey, A., Doel, P., Fanning, K., Font-Ribera, A., Forero-Romero, J.E., Gaztañaga, E., Gutierrez, G., Hahn, C., Honscheid, K., Howlett, C., Juneau, S., Levi, M.E., Meisner, A. ... Weaver, B.A. (2025). Exploring HOD-dependent systematics for the DESI 2024 Full-Shape galaxy clustering analysis. Journal of Cosmology and Astroparticle Physics, 2025 (9) 007. doi: 10.1088/1475-7516/2025/09/007
2025
Journal Article
DESI 2024 V: Full-Shape galaxy clustering 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 V: Full-Shape galaxy clustering from galaxies and quasars. Journal of Cosmology and Astroparticle Physics, 2025 (9) 008, 1-90. doi: 10.1088/1475-7516/2025/09/008
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
Supervision
Availability
- Dr Cullan Howlett is:
- Not available for supervision
Supervision history
Current supervision
-
Doctor Philosophy
Cosmology with the Dark Energy Spectroscopic Instrument
Principal Advisor
Other advisors: Professor Tamara Davis
-
Doctor Philosophy
Fundamental Plane distances from the Dark Energy Spectroscopic Instrument
Principal Advisor
Other advisors: Professor Tamara Davis
-
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
-
Doctor Philosophy
Direct detection of dark matter and exotic physics through atomic systems
Associate Advisor
Other advisors: Associate Professor Jacinda Ginges, Dr Benjamin Roberts
Completed supervision
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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
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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
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