I am a PhD student in the astronomy group at FMF, working with Prof. Maruša Bradač. My research focuses on unveiling the nature of dark matter and probing high-redshift galaxies by exploiting gravitational lensing in massive galaxy clusters and the data from the James Webb Space Telescope (JWST). I obtained my Bachelor's degree in Physics at the University of Ljubljana and my Master's degree in Astrophysics at Ludwig Maximilian University in Munich. I am co-PI of JWST program "Silver Bullet for Dark Matter" and PI of the ESA PRODEX project Darklens: Strong gravitational lensing in the Bullet cluster with JWST. I am a builder and an active member of the CANUCS JWST survey, and am involved in the VENUS JWST survey.
Apart from my passion for research, I am committed to promoting science and astronomy through outreach activities. I have delivered several public talks and regularly participate in events at Astronomical observatory Ljubljana. I regularly contribute to translations of the Astronomy Picture of the Day (APOD) into Slovene. I have published an outreach article on JWST in Slovenian popular science journal Proteus (featured on the cover page), and participated in the Cosmic Voices project, in collaboration with Academy of Music Ljubljana.
My main area of research is strong gravitational lensing in galaxy clusters. By using JWST NIRCam imaging and NIRISS and NIRSpec spectroscopy I am building a new generation of lens models, constrained with large catalogs of multiply imaged background galaxies.
As a PI of the ESA PRODEX project Darklens: Strong gravitational lensing in the Bullet cluster with JWST and a co-PI of JWST program "Silver Bullet for Dark Matter", I am leading the lensing analysis of the Bullet Cluster - a famous cluster merger that has provided some of the most direct evidence for the existence of dark matter and for constraining dark matter properties. With the Darklens project and the new JWST data I aim to improve the strong lensing reconstruction and put the tightest constraint on dark matter self-interactions with the Bullet Cluster to date. In collaboration with our industrial partner Abelium we are furthermore developing methods to automatically detect multiply imaged galaxies in JWST data.
I am deeply involved in CAnadian NIRISS Unbiased Cluster Survey (CANUCS, PI Willott), a JWST cycle 1 GTO program targeting five massive galaxy clusters with 200h of observing time. In CANUCS, I am overseeing the lensing data products (lens models and magnification catalogues - which are available with CANUCS DR1). I have furthermore published the lens model of cluster MACS J0416.1−2403, constrained with the largest catalogues of spectroscopic multiple images in a cluster field to date, and am developing a lens model of the "Supernova Refsdal cluster" MACS J1149.5+2223. Recently, I have joined the lensing working group of the Vast Exploration for Nascent, Unexplored Sources (VENUS, PI Fujimoto) collaboration, a Cycle 4 JWST program targeting 60 galaxy clusters with almost 300 hours of observing time (the second largest JWST program to date).
- Rihtaršič, G., et al. (2025) "CANUCS: Constraining the MACS J0416.1-2403 strong lensing model with JWST NIRISS, NIRSpec, and NIRCam", A&A, 696, A15
- Rihtaršič, G., et al. (2024) "Environmental dependence of AGN activity and star formation in galaxy clusters from Magneticum simulations", A&A, 683, A57
- Limousin, M., et al. (incl. GR as the third author) (2025) "Testing Light Unaffiliated Mass Clumps in MACS 0416 on galaxy and galaxy cluster scales using JWST", accepted for publication in A&A, arXiv:2506.16034
- Sarrouh, G. T. E., et al. (incl. GR as the 11th author) (2025) "CANUCS/Technicolor Data Release 1: Imaging, Photometry, Slit Spectroscopy, and Stellar Population Parameters", submitted to ApJ, arXiv, arXiv:2506.21685
- Gledhill, R., et al. (incl. GR as the 4th author) (2024) "CANUCS: An Updated Mass and Magnification Model of A370 with JWST", ApJ, 973, 77
- Mowla, L., et al. (2024) "Formation of a low-mass galaxy from star clusters in a 600-million-year-old Universe", Nature, 636, 332
For the full publication list see NASA ADS.
