Dr Cullan Howlett

Research Fellow in Cosmology

Physics
Faculty of Science
c.howlett@uq.edu.au
0420766717

Overview

I am a 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 was or currently am a member of nearly all the largest surveys:

  • The Sloan Digital Sky Survey (SDSS) Baryon Acoustic Oscillation survey - mapped the positions of over 1,000,000 galaxies using the Sloan Telescope.
  • The Dark Energy Spectroscopic Instrument (DESI) survey being carried out on The 4-m Mayall Telescope in Arizona which will get positions for over 40,000,000 galaxies
  • The Dark Energy Survey (DES) that has finished taking images of over 300,000,000 galaxies using the Blanco Telescope in Chile
  • The Taipan Galaxy Survey a planned survey of over 1,000,000 galaxy positions and motions using the UK-Schmidt Telescope right here in Australia (Siding Spring in NSW)
  • The WALLABY survey using the Australian Square Kilometer Array Pathfinder also based in Australia (Murchison, WA), which will make a blind survey of over 500,000 galaxies
  • The 4-Metre Multi-Object Spectroscopic Telescope which is currently under planning for construction in Chile.

My research makes use of state-of-the art computing techniques to simulate the distributions of galaxies from these surveys on supercomputers. I then analyse these distributions using different statistical techniques to 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.

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-

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 testing this theory using large galaxy surveys
  • 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 that can be done in a fraction of the time, or on fewer processors.
  • New statistical methods for analysing distributions of galaxies
    I'm always on the lookout for new ways to analyse the distributions of galaxies that might hold new information on the physics that drives this distribution.
  • 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 tenets of physics (Einstein's theory of General Relativity or Quantum Mechanics). We don't know, but the answer is out there, and it's 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 we develop are cutting edge and can often be used in fields outside astronomy (for instance in finance, environmental science, and even tackling pandemics...)

Publications

  • Stöcker, Patrick, Balázs, Csaba, Bloor, Sanjay, Bringmann, Torsten, Gonzalo, Tomás E., Handley, Will, Hotinli, Selim, Howlett, Cullan, Kahlhoefer, Felix, Renk, Janina J., Scott, Pat, Vincent, Aaron C., White, Martin and The GAMBIT Cosmology Workgroup (2021). Strengthening the bound on the mass of the lightest neutrino with terrestrial and cosmological experiments. Physical Review D, 103 (12) 123508. doi: 10.1103/physrevd.103.123508

  • Glanville, Aaron, Howlett, Cullan and Davis, Tamara M. (2021). The effect of systematic redshift biases in BAO cosmology. Monthly Notices of the Royal Astronomical Society, 503 (3), 3510-3521. doi: 10.1093/mnras/stab657

  • Renk, Janina J., Stöcker, Patrick, Bloor, Sanjay, Hotinli, Selim, Balázs, Csaba, Bringmann, Torsten, Gonzalo, Tomás E., Handley, Will, Hoof, Sebastian, Howlett, Cullan, Kahlhoefer, Felix, Scott, Pat, Vincent, Aaron C. and White, Martin (2021). CosmoBit: A GAMBIT module for computing cosmological observables and likelihoods. Journal of Cosmology and Astroparticle Physics, 2021 (2) 022. doi: 10.1088/1475-7516/2021/02/022

View all Publications

Supervision

  • Doctor Philosophy

  • Doctor Philosophy

  • Doctor Philosophy

View all Supervision

Available Projects

  • Maps of the positions of millions of galaxies in our Universe are used to refine our understanding of its components and evolution. However, these experiments have left us with more questions than answers. What is the nature of dark energy and dark matter? Is Einstein’s theory of General Relativity correct on scales beyond our solar system?

    Upcoming surveys aim to answer these questions. But understanding how the distributions and motions of galaxies relate to fundamental physics and how to sift through this enormous amount of data to uncover the truth requires improving our analysis techniques and developing new ways to use the data.

    Several projects are available under this theme, with different emphasis on mathematical theory, data analysis or computer programming. The first is improving and speeding up methods for simulating the Universe on supercomputers. Another is developing new mathematical models for describing how galaxies cluster and move relative to each other. The final project involves using real measurements of the speed with which local galaxies are moving from the completed 2MTF and 6dFGSv surveys to test different gravitational models.

  • Gravitational waves are ripples in space-time that propogate away from massive compact objects as they merge, to hopefully, eventually, be detected here on Earth by the LIGO/Virgo gravitational wave detectors. Gravitational waves hold information on some of the most exotic objects in the Universe such as black holes and neutron stars. They can also be used to test cosmological models, particularly because they act as "Standard Sirens" - the gravitational waveform tells us how far away the merging objects are which then can be used to work out how fast the Universe is expanding and how fast it's large scale structures are growing.

    This project will look at techniques for extracting Standard Siren measurements from gravitational waves. In particular, developing simulated catalogues of gravitational wave events and then using these simulations to work out how best to extract cosmology from the real data. This project brings together a range of fields, from understanding the details of how black holes and neutron stars are formed, to theoretical modelling of future cosmology studies that might be possible once we have hundreds of gravitational waves.

View all Available Projects

Publications

Journal Article

  • Stöcker, Patrick, Balázs, Csaba, Bloor, Sanjay, Bringmann, Torsten, Gonzalo, Tomás E., Handley, Will, Hotinli, Selim, Howlett, Cullan, Kahlhoefer, Felix, Renk, Janina J., Scott, Pat, Vincent, Aaron C., White, Martin and The GAMBIT Cosmology Workgroup (2021). Strengthening the bound on the mass of the lightest neutrino with terrestrial and cosmological experiments. Physical Review D, 103 (12) 123508. doi: 10.1103/physrevd.103.123508

  • Glanville, Aaron, Howlett, Cullan and Davis, Tamara M. (2021). The effect of systematic redshift biases in BAO cosmology. Monthly Notices of the Royal Astronomical Society, 503 (3), 3510-3521. doi: 10.1093/mnras/stab657

  • Renk, Janina J., Stöcker, Patrick, Bloor, Sanjay, Hotinli, Selim, Balázs, Csaba, Bringmann, Torsten, Gonzalo, Tomás E., Handley, Will, Hoof, Sebastian, Howlett, Cullan, Kahlhoefer, Felix, Scott, Pat, Vincent, Aaron C. and White, Martin (2021). CosmoBit: A GAMBIT module for computing cosmological observables and likelihoods. Journal of Cosmology and Astroparticle Physics, 2021 (2) 022. doi: 10.1088/1475-7516/2021/02/022

  • Byun, Joyce, Franco, Felipe Oliveira, Howlett, Cullan, Bonvin, Camille and Obreschkow, Danail (2020). Constraining the growth rate of structure with phase correlations. Monthly Notices of the Royal Astronomical Society, 497 (2), 1765-1790. doi: 10.1093/mnras/staa2020

  • Koribalski, Bärbel S., Staveley-Smith, L., Westmeier, T., Serra, P., Spekkens, K., Wong, O. I., Lee-Waddell, K., Lagos, C. D.P., Obreschkow, D., Ryan-Weber, E. V., Zwaan, M., Kilborn, V., Bekiaris, G., Bekki, K., Bigiel, F., Boselli, A., Bosma, A., Catinella, B., Chauhan, G., Cluver, M. E., Colless, M., Courtois, H. M., Crain, R. A., de Blok, W. J.G., Dénes, H., Duffy, A. R., Elagali, A., Fluke, C. J., For, B. Q. ... Wolf, C. (2020). WALLABY – an SKA Pathfinder H I survey. Astrophysics and Space Science, 365 (7) 118. doi: 10.1007/s10509-020-03831-4

  • Howlett, Cullan and Davis, Tamara M. (2020). Standard siren speeds: improving velocities in gravitational-wave measurements of H0. Monthly Notices of the Royal Astronomical Society, 492 (3), 3803-3815. doi: 10.1093/mnras/staa049

  • Hinton, Samuel R., Howlett, Cullan and Davis, Tamara M. (2020). BARRY and the BAO Model Comparison. Monthly Notices of the Royal Astronomical Society, 493 (3), 4078-4093. doi: 10.1093/mnras/staa361

  • Pan, Hengxing, Obreschkow, Danail, Howlett, Cullan, Lagos, Claudia del P., Elahi, Pascal J., Baugh, Carlton and Gonzalez-Perez, Violeta (2020). Multiwavelength consensus of large-scale linear bias. Monthly Notices of the Royal Astronomical Society, 493 (1), 747-764. doi: 10.1093/mnras/staa222

  • Davis, Tamara M., Hinton, Samuel R., Howlett, Cullan and Calcino, Josh (2019). Can redshift errors bias measurements of the Hubble Constant?. Monthly Notices of the Royal Astronomical Society, 490 (2), 2948-2957. doi: 10.1093/mnras/stz2652

  • Qin, Fei, Howlett, Cullan and Staveley-Smith, Lister (2019). The redshift-space momentum power spectrum II: measuring the growth rate from the combined 2MTF and 6dFGSv surveys. Monthly Notices of the Royal Astronomical Society, 487 (4) stz1576, 5235-5247. doi: 10.1093/mnras/stz1576

  • Howlett, Cullan (2019). The redshift-space momentum power spectrum – I. Optimal estimation from peculiar velocity surveys. Monthly Notices of the Royal Astronomical Society, 487 (4) stz1403, 5209-5234. doi: 10.1093/mnras/stz1403

  • Hong, Tao, Staveley-Smith, Lister, Masters, Karen L, Springob, Christopher M, Macri, Lucas M, Koribalski, Bärbel S, Jones, D Heath, Jarrett, Tom H, Crook, Aidan C, Howlett, Cullan and Qin, Fei (2019). 2MTF - VII. 2MASS Tully-Fisher survey final data release: distances for 2,062 nearby spiral galaxies. Monthly Notices of the Royal Astronomical Society, 487 (2), 2061-2069. doi: 10.1093/mnras/stz1413

  • Qin, Fei, Howlett, Cullan, Staveley-Smith, Lister and Hong, Tao (2019). Bulk flow and shear in the local Universe: 2MTF and COSMICFLOWS-3. Monthly Notices of the Royal Astronomical Society, 482 (2), 1920-1930. doi: 10.1093/mnras/sty2826

  • Qin, Fei, Howlett, Cullan, Staveley-Smith, Lister and Hong, Tao (2018). Bulk flow in the combined 2MTF and 6dFGSv surveys. Monthly Notices of the Royal Astronomical Society, 477 (4), 5150-5166. doi: 10.1093/mnras/sty928

  • Ali, Kamran, Obreschkow, Danail, Howlett, Cullan, Bonvin, Camille, Llinares, Claudio, Oliveira Franco, Felipe and Power, Chris (2018). Cosmological constraints from fourier phase statistics. Monthly Notices of the Royal Astronomical Society, 479 (2), 2743-2753. doi: 10.1093/mnras/sty1696

  • Robotham, A. S. G. and Howlett, Cullan (2018). A short research note on calculating exact distribution functions and random sampling for the 3D NFW profile. Research Notes of the AAS, 2 (2), 55. doi: 10.3847/2515-5172/aacc70

  • Howlett, Cullan and Percival, Will J. (2017). Galaxy two-point covariance matrix estimation for next generation surveys. Monthly Notices of the Royal Astronomical Society, 472 (4), 4935-4952. doi: 10.1093/mnras/stx2342

  • Howlett, Cullan, Staveley-Smith, Lister, Elahi, Pascal J., Hong, Tao, Jarrett, Tom H., Jones, D. Heath, Koribalski, Barbel S., Macri, Lucas M., Masters, Karen L. and Springob, Christopher M. (2017). 2MTF-VI. Measuring the velocity power spectrum. Monthly Notices of the Royal Astronomical Society, 471 (3), 3135-3151. doi: 10.1093/mnras/stx1521

  • da Cunha, Elisabete, Hopkins, Andrew M., Colless, Matthew, Taylor, Edward N., Blake, Chris, Howlett, Cullan, Magoulas, Christina, Lucey, John R., Lagos, Claudia, Kuehn, Kyler, Gordon, Yjan, Barat, Dilyar, Bian, Fuyan, Wolf, Christian, Cowley, Michael J., White, Marc, Achitouv, Ixandra, Bilicki, Maciej, Bland-Hawthorn, Joss, Bolejko, Krzysztof, Brown, Michael J. I., Brown, Rebecca, Bryant, Julia, Croom, Scott, Davis, Tamara M., Driver, Simon P., Filipovic, Miroslav D., Hinton, Samuel R., Johnston-Hollitt, Melanie ... Watson, Fred (2017). The Taipan Galaxy Survey: Scientific Goals and Observing Strategy. Publications of the Astronomical Society of Australia, 34 e047, 1-28. doi: 10.1017/pasa.2017.41

  • Howlett, Cullan, Robotham, Aaron S. G., Lagos, Claudia D. P. and Kim, Alex G. (2017). Measuring the growth rate of structure with type IA supernovae from LSST. Astrophysical Journal, 847 (2) aa88c8, 128. doi: 10.3847/1538-4357/aa88c8

  • Howlett, Cullan, Staveley-Smith, Lister and Blake, Chris (2017). Cosmological forecasts for combined and next-generation peculiar velocity surveys. Monthly Notices of the Royal Astronomical Society, 464 (3), 2517-2544. doi: 10.1093/mnras/stw2466

  • Andersen, P., Davis, T. M. and Howlett, C. (2016). Cosmology with peculiar velocities: observational effects. Monthly Notices of the Royal Astronomical Society, 463 (4), 4083-4092. doi: 10.1093/mnras/stw2252

  • Aubourg, Éric, Bailey, Stephen, Bautista, Julian E., Beutler, Florian, Bhardwaj, Vaishali, Bizyaev, Dmitry, Blanton, Michael, Blomqvist, Michael, Bolton, Adam S., Bovy, Jo, Brewington, Howard, Brinkmann, J., Brownstein, Joel R., Burden, Angela, Busca, Nicolás G., Carithers, William, Chuang, Chia-Hsun, Comparat, Johan, Croft, Rupert A. C., Cuesta, Antonio J., Dawson, Kyle S., Delubac, Timothée, Eisenstein, Daniel J., Font-Ribera, Andreu, Ge, Jian, Le Goff, J. M., Gontcho, Satya Gontcho A., Gott, J. Richard, Gunn, James E. ... Zhao, Gong-Bo (2015). Cosmological implications of baryon acoustic oscillation measurements. Physical Review D - Particles, Fields, Gravitation and Cosmology, 92 (12) 123516. doi: 10.1103/PhysRevD.92.123516

  • Burden, A., Percival, W. J. and Howlett, C. (2015). Reconstruction in Fourier space. Monthly Notices of the Royal Astronomical Society, 453 (1), 456-468. doi: 10.1093/mnras/stv1581

  • Liske, J., Baldry, I. K., Driver, P., Tuffs, R. J., Alpaslan, M., Andrae, E., Brough, S., Cluver, M. E., Grootes, M. W., Gunawardhana, M. L. P., Kelvin, L. S., Loveday, J., Robotham, A. S. G., Taylor, E. N., Bamford, S. P., Bland-Hawthorn, J., Brown, M. J. I., Drinkwater, M. J., Hopkins, A. M., Meyer, M. J., Norberg, P., Peacock, J. A., Agius, N. K., Andrews, S. K., Bauer, A. E., Ching, J. H. Y., Colless, M., Conselice, C. J., Croom, S. M. ... Wright, A. H. (2015). Galaxy and mass assembly (GAMA): End of survey report and data release 2. Monthly Notices of the Royal Astronomical Society, 452 (2), 2087-2126. doi: 10.1093/mnras/stv1436

  • Howlett, C., Manera, M. and Percival, W. J. (2015). L-PICOLA: a parallel code for fast dark matter simulation. Astronomy and Computing, 12, 109-126. doi: 10.1016/j.ascom.2015.07.003

  • Ross, Ashley J., Samushia, Lado, Howlett, Cullan, Percival, Will J., Burden, Angela and Manera, Marc (2015). The clustering of the SDSS DR7 main Galaxy sample - I. A 4 per cent distance measure at z=0.15. Monthly Notices of the Royal Astronomical Society, 449 (1), 835-847. doi: 10.1093/mnras/stv154

  • Howlett, Cullan, Ross, Ashley J., Samushia, Lado, Percival, Will J. and Manera, Marc (2015). The clustering of the SDSS main galaxy sample - II. Mock galaxy catalogues and a measurement of the growth of structure from redshift space distortions at z=0.15. Monthly Notices of the Royal Astronomical Society, 449 (1), 848-866. doi: 10.1093/mnras/stu2693

  • Manera, Marc, Samushia, Lado, Tojeiro, Rita, Howlett, Cullan, Ross, Ashley J., Percival, Will J., Gil-Marín, Hector, Brownstein, Joel R., Burden, Angela and Montesano, Francesco (2015). The clustering of galaxies in the SDSS-III baryon oscillation spectroscopic survey: Mock galaxy catalogues for the low-redshift sample. Monthly Notices of the Royal Astronomical Society, 447 (1), 437-445. doi: 10.1093/mnras/stu2465

  • Tojeiro, Rita, Ross, Ashley J., Burden, Angela, Samushia, Lado, Manera, Marc, Percival, Will J., Beutler, Florian, Brinkmann, J., Brownstein, Joel R., Cuesta, Antonio J., Dawson, Kyle, Eisenstein, Daniel J., Ho, Shirley, Howlett, Cullan, McBride, Cameron K., Montesano, Francisco, Olmstead, Matthew D., Parejko, John K., Reid, Beth, Sanchez, Ariel G., Schlegel, David J., Schneider, Donald P., Tinker, Jeremy L., Magana, Mariana Vargas and White, Martin (2014). The clustering of galaxies in the SDSS-III Baryon Oscillation Spectroscopic Survey: galaxy clustering measurements in the low-redshift sample of Data Release 11. Monthly Notices of the Royal Astronomical Society, 440 (3), 2222-2237. doi: 10.1093/mnras/stu371

  • Anderson, Lauren, Aubourg, Élric, Bailey, Stephen, Beutler, Florian, Bhardwaj, Vaishali, Blanton, Michael, Bolton, Adam S., Brinkmann, J., Brownstein, Joel R., Burden, Angela, Chuang, Chia-Hsun, Cuesta, Antonio J., Dawson, Kyle S., Eisenstein, Daniel J., Escoffier, Stephanie, Gunn, James E., Guo, Hong, Ho, Shirley, Honscheid, Klaus, Howlett, Cullan, Kirkby, David, Lupton, Robert H., Manera, Marc, Maraston, Claudia, McBride, Cameron K., Mena, Olga, Montesano, Francesco, Nichol, Robert C., Nuza, Sebastián E. ... Zhao, Gong-Bo (2014). The clustering of galaxies in the SDSS-III baryon oscillation spectroscopic survey: Baryon acoustic oscillations in the data releases 10 and 11 galaxy samples. Monthly Notices of the Royal Astronomical Society, 441 (1), 24-62. doi: 10.1093/mnras/stu523

  • Howlett, Cullan, Lewis, Antony, Hall, Alex and Challinor, Anthony (2012). CMB power spectrum parameter degeneracies in the era of precision cosmology. Journal of Cosmology and Astroparticle Physics, 2012 (4) 027, 027-027. doi: 10.1088/1475-7516/2012/04/027

Conference Publication

  • Manera, M., Percival, W. J., Ross, Ashley, Tojeiro, R., Samushia, L., Howlett, C., Vargas-Magaña, M., Burden, A. and SDSS-III BOSS Galaxy Working Group (2014). Understanding cosmological measurements with a large number of mock galaxy catalogues. 306th Symposium of The International-Astronomical-Union (IAU), Lisbon, Portugal, 25-29 May 2014. CAMBRIDGE: Cambridge University Press (CUP). doi: 10.1017/s1743921314013738

PhD and MPhil Supervision

Current Supervision

  • Doctor Philosophy — Principal Advisor

    Other advisors:

  • Doctor Philosophy — Principal Advisor

    Other advisors:

  • Doctor Philosophy — Principal Advisor

    Other advisors:

Possible Research Projects

Note for students: The possible research projects listed on this page may not be comprehensive or up to date. Always feel free to contact the staff for more information, and also with your own research ideas.

  • Maps of the positions of millions of galaxies in our Universe are used to refine our understanding of its components and evolution. However, these experiments have left us with more questions than answers. What is the nature of dark energy and dark matter? Is Einstein’s theory of General Relativity correct on scales beyond our solar system?

    Upcoming surveys aim to answer these questions. But understanding how the distributions and motions of galaxies relate to fundamental physics and how to sift through this enormous amount of data to uncover the truth requires improving our analysis techniques and developing new ways to use the data.

    Several projects are available under this theme, with different emphasis on mathematical theory, data analysis or computer programming. The first is improving and speeding up methods for simulating the Universe on supercomputers. Another is developing new mathematical models for describing how galaxies cluster and move relative to each other. The final project involves using real measurements of the speed with which local galaxies are moving from the completed 2MTF and 6dFGSv surveys to test different gravitational models.

  • Gravitational waves are ripples in space-time that propogate away from massive compact objects as they merge, to hopefully, eventually, be detected here on Earth by the LIGO/Virgo gravitational wave detectors. Gravitational waves hold information on some of the most exotic objects in the Universe such as black holes and neutron stars. They can also be used to test cosmological models, particularly because they act as "Standard Sirens" - the gravitational waveform tells us how far away the merging objects are which then can be used to work out how fast the Universe is expanding and how fast it's large scale structures are growing.

    This project will look at techniques for extracting Standard Siren measurements from gravitational waves. In particular, developing simulated catalogues of gravitational wave events and then using these simulations to work out how best to extract cosmology from the real data. This project brings together a range of fields, from understanding the details of how black holes and neutron stars are formed, to theoretical modelling of future cosmology studies that might be possible once we have hundreds of gravitational waves.