Harley Katz

Beecroft Fellow · Co-founder of Probably Genetic · Forbes 30 Under 30 · PhD Astrophysics · harley.katz@physics.ox.ac.uk

In short, I tackle hard problems with large computers.

Current Projects

Feel free to reach out for collaboration on any of these topics.


Transforming our understanding of the ISM and CGM with RAMSES-RTZ

Awarded >50M CPUh on the UK's DiRAC facilities, MEGATRON is the first cosmological simulation to self-consistently model the non-equilibrium chemistry and heating/cooling processes in the interstellar medium for nearly 100 atoms, ions, and molecules coupled to on-the-fly radiation transfer. Complete with state-of-the-art modules for galaxy formation and stellar feedback, including the formation and enrichment from Population III stars, MEGATRON models the formation of a Milky Way-like galaxy from the earliest epochs until cosmic noon.

SPHINX20 Public Data Release

Apples-to-apples comparisons between high-redshift simulations and JWST observations

An ambitious project to completely forward-model the spectra and photometry from the largest full-box cosmological radiation hydrodynamcis simulation of reionization with a resolved ISM.

Exascale Gravity

A new gravity algorithm without all-to-all communication

The next generation of exascale codes require us to rethink even our most basic algorithms. This project is in its infant stages and uses a purely-local method to solve gravity in a cosmological setting.


University of Cambridge

PhD in Astrophysics
October 2013 - September 2017

University of Maryland, College Park

Double Degree, BS in Physics, BS in Astronomy
August 2009 - May 2013

Astrophysics Publications

  • Katz, H., Kimm, T., Ellis, R. S., Devriendt, J., & Slyz, A., 'The challenges of identifying Population III stars in the early Universe', MNRAS, 524, 351 (2023).
  • Katz, H., Saxena, A., Cameron, A. J., Carniani, S., Bunker, A. J., Arribas, S., Bhatawdekar, R., Bowler, R. A. A., Boyett, K. N. K., Cresci, G., Curtis-Lake, E., D'Eugenio, F., Kumari, N., Looser, T. J., Maiolino, R., Übler, H., Willott, C., & Witstok, J., 'First insights into the ISM at z > 8 with JWST: possible physical implications of a high [O III] λ4363/[O III] λ5007', MNRAS, 518, 592 (2023).
  • Katz, H., Saxena, A., Rosdahl, J., Kimm, T., Blaizot, J., Garel, T., Michel-Dansac, L., Haehnelt, M., Ellis, R. S., Pentericci, L., Devriendt, J., & Slyz, A., 'Two modes of LyC escape from bursty star formation: implications for [C II] deficits and the sources of reionization', MNRAS, 518, 270 (2023).
  • Katz, H., Liu, S., Kimm, T., Rey, M. P., Andersson, E. P., Cameron, A. J., Rodriguez-Montero, F., Agertz, O., Devriendt, J., & Slyz, A., 'PRISM: A Non-Equilibrium, Multiphase Interstellar Medium Model for Radiation Hydrodynamics Simulations of Galaxies', arXiv, arXiv:2211.04626 (2022).
  • Katz, H., Garel, T., Rosdahl, J., Mauerhofer, V., Kimm, T., Blaizot, J., Michel-Dansac, L., Devriendt, J., Slyz, A., & Haehnelt, M., 'Mg II in the JWST era: a probe of Lyman continuum escape?', MNRAS, 515, 4265 (2022).
  • Katz, H., 'RAMSES-RTZ: non-equilibrium metal chemistry and cooling coupled to on-the-fly radiation hydrodynamics', MNRAS, 512, 348 (2022).
  • Katz, H., Rosdahl, J., Kimm, T., Garel, T., Blaizot, J., Haehnelt, M. G., Michel-Dansac, L., Martin-Alvarez, S., Devriendt, J., Slyz, A., Teyssier, R., Ocvirk, P., Laporte, N., & Ellis, R., 'The nature of high [O III]88 μ m/[C II]158 μm galaxies in the epoch of reionization: Low carbon abundance and a top-heavy IMF?', MNRAS, 510, 5603 (2022).
  • Katz, H., Martin-Alvarez, S., Rosdahl, J., Kimm, T., Blaizot, J., Haehnelt, M. G., Michel-Dansac, L., Garel, T., Oñorbe, J., Devriendt, J., Slyz, A., Attia, O., & Teyssier, R., 'Introducing SPHINX-MHD: the impact of primordial magnetic fields on the first galaxies, reionization, and the global 21-cm signal', MNRAS, 507, 1254 (2021).
  • Katz, H., Ďurovčíková, D., Kimm, T., Rosdahl, J., Blaizot, J., Haehnelt, M. G., Devriendt, J., Slyz, A., Ellis, R., & Laporte, N., 'New methods for identifying Lyman continuum leakers and reionization-epoch analogues', MNRAS, 498, 164 (2020).
  • Katz, H., Ramsoy, M., Rosdahl, J., Kimm, T., Blaizot, J., Haehnelt, M. G., Michel-Dansac, L., Garel, T., Laigle, C., Devriendt, J., & Slyz, A., 'How to quench a dwarf galaxy: The impact of inhomogeneous reionization on dwarf galaxies and cosmic filaments', MNRAS, 494, 2200 (2020).
  • Katz, H., Galligan, T. P., Kimm, T., Rosdahl, J., Haehnelt, M. G., Blaizot, J., Devriendt, J., Slyz, A., Laporte, N., & Ellis, R., 'Probing cosmic dawn with emission lines: predicting infrared and nebular line emission for ALMA and JWST', MNRAS, 487, 5902 (2019).
  • Katz, H., Laporte, N., Ellis, R. S., Devriendt, J., & Slyz, A., 'Probing cosmic dawn: modelling the assembly history, SEDs, and dust content of selected z ∼ 9 galaxies', MNRAS, 484, 4054 (2019).
  • Katz, H., Martin-Alvarez, S., Devriendt, J., Slyz, A., & Kimm, T., 'Magnetogenesis at Cosmic Dawn: tracing the origins of cosmic magnetic fields', MNRAS, 484, 2620 (2019).
  • Katz, H., Desmond, H., McGaugh, S., & Lelli, F., 'The tight empirical relation between dark matter halo mass and flat rotation velocity for late-type galaxies', MNRAS, 483, L98 (2019).
  • Katz, H., Kimm, T., Haehnelt, M. G., Sijacki, D., Rosdahl, J., & Blaizot, J., 'Tracing the sources of reionization in cosmological radiation hydrodynamics simulations', MNRAS, 483, 1029 (2019).
  • Katz, H., Desmond, H., Lelli, F., McGaugh, S., Di Cintio, A., Brook, C., & Schombert, J., 'Stellar feedback and the energy budget of late-type Galaxies: missing baryons and core creation', MNRAS, 480, 4287 (2018).
  • Katz, H., Kimm, T., Haehnelt, M., Sijacki, D., Rosdahl, J., & Blaizot, J., 'A Census of the LyC photons that form the UV background during reionization', MNRAS, 478, 4986 (2018).
  • Katz, H., Kimm, T., Sijacki, D., & Haehnelt, M. G., 'Interpreting ALMA observations of the ISM during the epoch of reionization', MNRAS, 468, 4831 (2017).
  • Katz, H., Lelli, F., McGaugh, S. S., Di Cintio, A., Brook, C. B., & Schombert, J. M., 'Testing feedback-modified dark matter haloes with galaxy rotation curves: estimation of halo parameters and consistency with ΛCDM scaling relations', MNRAS, 466, 1648 (2017).
  • Katz, H., Sijacki, D., & Haehnelt, M. G., 'Seeding high-redshift QSOs by collisional runaway in primordial star clusters', MNRAS, 451, 2352 (2015).
  • Katz, H., Sijacki, D., & Haehnelt, M., 'Seeding High Redshift QSOs by Collisional Runaway in Primordial Star Clusters', IAUGA, 29, 2230030 (2015).
  • Katz, H., & Ricotti, M., 'Clues on the missing sources of reionization from self-consistent modelling of Milky Way and dwarf galaxy globular clusters', MNRAS, 444, 2377 (2014).
  • Katz, H., McGaugh, S. S., Sellwood, J. A., & de Blok, W. J. G., 'The formation of spiral galaxies: adiabatic compression with Young's algorithm and the relation of dark matter haloes to their primordial antecedents', MNRAS, 439, 1897 (2014).
  • Katz, H., & Ricotti, M., 'Two epochs of globular cluster formation from deep field luminosity functions: implications for reionization and the Milky Way satellites', MNRAS, 432, 3250 (2013).
  • Katz, H., McGaugh, S., Teuben, P., & Angus, G. W., 'Galaxy Cluster Bulk Flows and Collision Velocities in QUMOND', ApJ, 772, 10 (2013).

  • Blaizot, J., Garel, T., Verhamme, A., Katz, H., Kimm, T., Michel-Dansac, L., Mitchell, P. D., Rosdahl, J., & Trebitsch, M., 'Simulating the diversity of shapes of the Lyman-α line', MNRAS, 523, 3749 (2023).
  • Cameron, A. J., Katz, H., Rey, M. P., & Saxena, A., 'Nitrogen enhancements 440 Myr after the big bang: supersolar N/O, a tidal disruption event, or a dense stellar cluster in GN-z11?', MNRAS, 523, 3516 (2023).
  • Cameron, A. J., Katz, H., & Rey, M. P., 'A novel approach to correcting Te-based mass-metallicity relations', MNRAS, 522, L89 (2023).
  • Steinhardt, C. L., Sneppen, A., Clausen, T., Katz, H., Rey, M. P., & Stahlschmidt, J., 'The Highest-Redshift Balmer Breaks as a Test of ΛCDM', arXiv, arXiv:2305.15459 (2023).
  • Choustikov, N., Katz, H., Saxena, A., Cameron, A. J., Devriendt, J., Slyz, A., Rosdahl, J., Blaizot, J., & Michel-Dansac, L., 'The Physics of Indirect Estimators of Lyman Continuum Escape and their Application to High-Redshift JWST Galaxies', arXiv, arXiv:2304.08526 (2023).
  • Witten, C., Laporte, N., Martin-Alvarez, S., Sijacki, D., Yuan, Y., Haehnelt, M. G., Baker, W., Dunlop, J. S., Ellis, R. S., Grogin, N., Illingworth, G., Katz, H., Koekemoer, A. M., Magee, D., Maiolino, R., McClymont, W., Pérez-González, P. G., Puskas, D., Roberts-Borsani, G., Santini, P., & Simmonds, C., 'Deciphering Lyman-α Emission Deep into the Epoch of Reionisation', arXiv, arXiv:2303.16225 (2023).
  • Rey, M. P., Katz, H. B., Cameron, A. J., Devriendt, J., & Slyz, A., 'Boosting galactic outflows with enhanced resolution', arXiv, arXiv:2302.08521 (2023).
  • Witten, C. E. C., Laporte, N., & Katz, H., 'Evidence for a Low Lyman Continuum Escape Fraction in Three Massive, Ultraviolet-bright Galaxies at z > 7', ApJ, 944, 61 (2023).
  • Saxena, A., Cryer, E., Ellis, R. S., Pentericci, L., Calabrò, A., Mascia, S., Saldana-Lopez, A., Schaerer, D., Katz, H., Llerena, M., & Amorín, R., 'Strong C IV emission from star-forming galaxies: a case for high Lyman continuum photon escape', MNRAS, 517, 1098 (2022).
  • Rosdahl, J., Blaizot, J., Katz, H., Kimm, T., Garel, T., Haehnelt, M., Keating, L. C., Martin-Alvarez, S., Michel-Dansac, L., & Ocvirk, P., 'LyC escape from SPHINX galaxies in the Epoch of Reionization', MNRAS, 515, 2386 (2022).
  • Han, D., Kimm, T., Katz, H., Devriendt, J., & Slyz, A., 'Impact of Radiation Feedback on the Formation of Globular Cluster Candidates during Cloud-Cloud Collisions', ApJ, 935, 53 (2022).
  • Martin-Alvarez, S., Devriendt, J., Slyz, A., Sijacki, D., Richardson, M. L. A., & Katz, H., 'Towards convergence of turbulent dynamo amplification in cosmological simulations of galaxies', MNRAS, 513, 3326 (2022).
  • Maji, M., Verhamme, A., Rosdahl, J., Garel, T., Blaizot, J., Mauerhofer, V., Pittavino, M., Victoria Feser, M.-P., Chuniaud, M., Kimm, T., Katz, H., & Haehnelt, M., 'Predicting Lyman-continuum emission of galaxies using their physical and Lyman-α emission properties', A&A, 663, A66 (2022).
  • Lee, J., Kimm, T., Blaizot, J., Katz, H., Lee, W., Sheen, Y.-K., Devriendt, J., & Slyz, A., 'Simulating Jellyfish Galaxies: A Case Study for a Gas-rich Dwarf Galaxy', ApJ, 928, 144 (2022).
  • Trebitsch, M., Dubois, Y., Volonteri, M., Pfister, H., Cadiou, C., Katz, H., Rosdahl, J., Kimm, T., Pichon, C., Beckmann, R. S., Devriendt, J., & Slyz, A., 'The OBELISK simulation: Galaxies contribute more than AGN to H I reionization of protoclusters', A&A, 653, A154 (2021).
  • Martin-Alvarez, S., Katz, H., Sijacki, D., Devriendt, J., & Slyz, A., 'Unravelling the origin of magnetic fields in galaxies', MNRAS, 504, 2517 (2021).
  • Attia, O., Teyssier, R., Katz, H., Kimm, T., Martin-Alvarez, S., Ocvirk, P., & Rosdahl, J., 'Cosmological magnetogenesis: the Biermann battery during the Epoch of reionization', MNRAS, 504, 2346 (2021).
  • Garel, T., Blaizot, J., Rosdahl, J., Michel-Dansac, L., Haehnelt, M. G., Katz, H., Kimm, T., & Verhamme, A., 'Ly α as a tracer of cosmic reionization in the SPHINX radiation-hydrodynamics cosmological simulation', MNRAS, 504, 1902 (2021).
  • Lee, J., Kimm, T., Katz, H., Rosdahl, J., Devriendt, J., & Slyz, A., 'Dual Effects of Ram Pressure on Star Formation in Multiphase Disk Galaxies with Strong Stellar Feedback', ApJ, 905, 31 (2020).
  • Ďurovčíková, D., Katz, H., Bosman, S. E. I., Davies, F. B., Devriendt, J., & Slyz, A., 'Reionization history constraints from neural network based predictions of high-redshift quasar continua', MNRAS, 493, 4256 (2020).
  • Laporte, N., Katz, H., Ellis, R. S., Lagache, G., Bauer, F. E., Boone, F., Inoue, A. K., Hashimoto, T., Matsuo, H., Mawatari, K., & Tamura, Y., 'The absence of [C II] 158 μm emission in spectroscopically confirmed galaxies at z > 8', MNRAS, 487, L81 (2019).
  • Kimm, T., Blaizot, J., Garel, T., Michel-Dansac, L., Katz, H., Rosdahl, J., Verhamme, A., & Haehnelt, M., 'Understanding the escape of LyC and Lyα photons from turbulent clouds', MNRAS, 486, 2215 (2019).
  • Lelli, F., McGaugh, S. S., Schombert, J. M., Desmond, H., & Katz, H., 'The baryonic Tully-Fisher relation for different velocity definitions and implications for galaxy angular momentum', MNRAS, 484, 3267 (2019).
  • Desmond, H., Katz, H., Lelli, F., & McGaugh, S., 'Uncorrelated velocity and size residuals across galaxy rotation curves', MNRAS, 484, 239 (2019).
  • Galligan, T. P., Katz, H., Kimm, T., Rosdahl, J., Blaizot, J., Devriendt, J., & Slyz, A., 'deepCool: Fast and Accurate Estimation of Cooling Rates in Irradiated Gas with Artificial Neural Networks', arXiv, arXiv:1901.01264 (2019).
  • Rosdahl, J., Katz, H., Blaizot, J., Kimm, T., Michel-Dansac, L., Garel, T., Haehnelt, M., Ocvirk, P., & Teyssier, R., 'The SPHINX cosmological simulations of the first billion years: the impact of binary stars on reionization', MNRAS, 479, 994 (2018).
  • Kimm, T., Haehnelt, M., Blaizot, J., Katz, H., Michel-Dansac, L., Garel, T., Rosdahl, J., & Teyssier, R., 'Impact of Lyman alpha pressure on metal-poor dwarf galaxies', MNRAS, 475, 4617 (2018).
  • Kimm, T., Katz, H., Haehnelt, M., Rosdahl, J., Devriendt, J., & Slyz, A., 'Feedback-regulated star formation and escape of LyC photons from mini-haloes during reionization', MNRAS, 466, 4826 (2017).