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Matthee Group

Astrophysics of Galaxies

Galaxies such as our own Milky Way are the largest bound structures in our Universe and consist of gas, stars, planets, black holes and dark matter. The astrophysical processes that occur in galaxies happened to every atom in our body and therefore teach us about our own cosmic origins. The Matthee group investigates the physical mechanisms that determine how galaxies and their constituents form and evolve using observations of the very distant Universe.

Galaxies form following the collapse of small perturbations in the initial density distribution that formed in the Big Bang. While the physics of gravitational collapse is well understood, detailed feedback processes that happen within galaxies, such as the formation of stars, supernova explosions and the growth of supermassive black holes are poorly understood, while they have significant impact on the fate of galaxies and the stars and planets within them. The Matthee group uses observations of galaxies in the distant Universe to look back in time and probe the properties of the young massive stars in these galaxies responsible for the creation of the majority of heavy elements and the production of most of the ionizing radiation in the early Universe, and their impact on interstellar gas clouds. Matthee uses the largest telescopes on Earth (such as ESO’s Very Large Telescope in Chile) and in space (such as NASA/ESA/CSA’s James Webb Space Telescope) to find and study the first generations of galaxies and focus on empirically mapping the interplay between these galaxies and intergalactic gas in the so called reionization epoch that was the last major phase transition of matter in the Universe and happened only a few hundred million years after the Big Bang. Matthee also uses large cosmological hydrodynamical simulations to investigate the relation between structure formation, galaxies’ growth rates and their imprints on chemical enrichment.

Open positions

Applications are currently open for PhD and postdoc positions in the Matthee group! 
Prospective PhD students: please apply through
Prospective postdoctoral fellows: please contact

Current Projects

Galaxies as tracers and agents of cosmic reionization
The Matthee group involved in several programs using the infrared capabilities of the JWST to identify young emission-line galaxies in the early Universe through Halpha and [OIII] emission. We will use these measurements to accurately investigate:

  • the amount of star formation in the early Universe,
  • the metal-enrichment process in and around early galaxies
  • the connection between galaxies and intergalactic gas

Matthee is leading an ERC StG to measure the total ionising budget from young galaxies in the early Universe and self-consistently trace the topology and timing of cosmic reionization. In addition to JWST data, this project also benefits from ground-based observations of the Lyman-alpha emission line from galaxies which traces when and by how much galaxies leak ionizing photons.

The properties of the first stars and black holes in the first galaxies
In the future, the Matthee group will build upon the galaxies identified in the current projects and plans to use extremely sensitive observations, for example with the Extremely Large Telescope, to measure the temperatures, masses and chemical compositions of the first generations that formed in the Universe.


Wang B, Leja J, De Graaff A, Brammer GB, Weibel A, Van Dokkum P, Baggen JFW, Suess KA, Greene JE, Bezanson R, Cleri NJ, Hirschmann M, Labbé I, Matthee JJ, Mcconachie I, Naidu RP, Nelson E, Oesch PA, Setton DJ, Williams CC. 2024. RUBIES: Evolved stellar populations with extended formation histories at z ∼ 7-8 in candidate massive galaxies identified with JWST/NIRSpec. Astrophysical Journal Letters. 969(1), L13. View

Heintz KE, Watson D, Brammer G, Vejlgaard S, Hutter A, Strait VB, Matthee JJ, Oesch PA, Jakobsson P, Tanvir NR, Laursen P, Naidu RP, Mason CA, Killi M, Jung I, Hsiao TYY, Abdurro’Uf U, Coe D, Haro PA, Finkelstein SL, Toft S. 2024. Strong damped Lyman-a absorption in young star-forming galaxies at redshifts 9 to 11. Science. 384(6698), 890–894. View

Yue M, Eilers AC, Simcoe RA, Mackenzie R, Matthee JJ, Kashino D, Bordoloi R, Lilly SJ, Naidu RP. 2024. EIGER. V. Characterizing the host galaxies of luminous quasars at z ≳ 6. Astrophysical Journal. 966(2), 176. View

Matthee JJ, Golling C, Mackenzie R, Pezzulli G, Lilly S, Schaye J, Bacon R, Kusakabe H, Urrutia T, Boogaard L, Brinchmann J, Maseda MV, Garel T, Bouché NF, Wisotzki L. 2024. Large-scale excess H I absorption around z ≈ 4 galaxies detected in a background galaxy spectrum in the MUSE eXtremely deep field. Monthly Notices of the Royal Astronomical Society. 529(3), 2794–2806. View

Pensabene A, Cantalupo S, Cicone C, Decarli R, Galbiati M, Ginolfi M, De Beer S, Fossati M, Fumagalli M, Lazeyras T, Pezzulli G, Travascio A, Wang W, Matthee JJ, Maseda MV. 2024. ALMA survey of a massive node of the Cosmic Web at z ∼ 3: I. Discovery of a large overdensity of CO emitters. Astronomy and Astrophysics. 684, A119. View

View All Publications

ReX-Link: Jorryt Matthee


Since 2023 Assistant Professor, Institute of Science and Technology Austria (ISTA)
2018-2023 Postdoctoral researcher (Zwicky Fellow), ETH Zurich, Switzerland
2018 PhD, Leiden University, The Netherlands

Selected Distinctions

2022, ERC Starting Grant
2020, MERAC Prize for best PhD Thesis in Observational Astrophysics
2019, IAU PhD Prize, Division J Galaxies and cosmology, International Astronomical Union
2019, C.J. Kok Jury Award, Best PhD thesis, Science Faculty, Leiden University

Additional Information

Download CV
Matthee Group Website

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