The galaxy luminosity and mass function in Euclid clusters and protoclusters: cosmology and galaxy evolution
Supervisor: Prof. Simona Mei, APC ( https://www.linkedin.com/in/simona-mei-1721bb3a/ )
Co-Supervisor: Dr. Anand Raichoor
Astroparticule et Cosmologie, Physics Department, Université Paris Cité; Center Pierre Binetruy/UC Berkeley, USA/Stanford University
The Euclid space mission of the European Space Agency (ESA) is the flagship cosmology mission for the coming decade, giving the European community a leading role in the field. The mission aims to probe the nature of the dark sector: dark energy and dark matter: https://www.esa.int/Science_Exploration/Space_Science/Euclid
Euclid was launched in July 2023 for a 6 year mission. By the end of the mission, Euclid will have established the strongest constraints to date on the evolution of dark energy (its equation of state), a crucial step toward better understanding its nature. In addition, the Euclid survey data will enable a wide range of astrophysical studies of cosmic structures. Euclid will carry out a photometric survey (one band in the visible and three bands in the near-infrared) and a spectroscopic survey (slitless, in the near-infrared) of galaxies over the entire extragalactic sky outside the Galactic plane (about 15,000 square degrees). The mission will apply two primary probes of the dark sector — gravitational lensing shear (WL) and the distribution of galaxies (including baryon acoustic oscillations, BAO, and redshift-space distortions, RSD) — as well as secondary probes such as the evolution of galaxy clusters and the cross-correlation between the distribution of galaxies and measurements of the cosmic microwave background (CMB).
To use galaxy clusters as a cosmological probe, we need to measure their mass in a very accurate way. Weak lensing mass estimations will be possible for the most massive clusters. However, we will also need cluster mass measurements that use the cluster galaxy properties, such as the total cluster mass derived from the cluster galaxy mass and luminosity functions. These measurements will also permit us to gain insight in galaxy formation and evolution in dense environments, quenching and morphological transformations, a field in which Euclid observations will be determinant.
A first data release happened in November 2024 (Euclid Q1), and was followed by a more extensive data release to the consortium (Euclid DR1) in November 2025. Our team at APC is responsible for developing software for measuring the cluster galaxy mass and luminosity functions and for the publication of the Euclid DR1 cluster galaxy mass and luminosity functions.
The Ph.D. student will be responsible for measuring the cluster galaxy mass and luminosity functions with Euclid DR1 data and to publish scientific results related to these measurements in one refereed paper. S.he will use software developed by our team engineers and will write the software necessary for the scientific analysis. The Euclid DR1 will permit us to measure luminosity and mass functions up to redshift z~1-1.5. At redshift z~2 and beyond, the Ph.D. student will combine Euclid and DESI observations to measure high redshift galaxy luminosity functions.
This work is in collaboration with colleagues at Stanford University, in Stanford, USA/Center Pierre Binetruy (CPB)/UC Berkeley. The Ph.D. student will work within the Euclid team at APC, which include 2 Ph.D. students, and a postdoc, in the larger context of the Euclid consortium, the APC (https://apc.u-paris.fr/) Cosmology team (https://apc.u-paris.fr/fr/cosmologie), and the CPB (https://www.cpb.in2p3.fr/).
The Ph.D. candidates should contact Simona Mei (mei@apc.in2p3.fr) and Anand Raichoor (raichoor@apc.in2p3.fr). If you are an international student, we will need to apply for international grants as soon as possible.