Cosmology with Galaxy Clusters

Principal Investigator: Stefano Borgani


  • Structures in the Universe
  • Theory and Phenomenology of Gravity

Abstract: This line of research is devoted to studying clusters of galaxies as tracers of cosmic evolution and as tools to constrain cosmological models. Methods based on redshift- and mass-dependent number counts, statistics of the large-scale distribution of galaxy clusters, recovery of mass profiles from gravitational lensing, dynamical analysis of member galaxies and of the intra-cluster medium will be used to set constraints on cosmological parameters of the standard LambdaCDM model and upper limits on possible modifications of GR.


Clusters of galaxies have the potential of tightly constrain cosmological models in different ways: (1) The redshift evolution of cluster number counts is a highly sensitive probe of both the growth rate of cosmic perturbations and of the underlying expansion history; (2) Galaxy Clusters are amplified tracers of the large-scale structure of the Universe and, as such, they are powerful probes of the underlying cosmological model; (3) The cluster internal structure, probed by a variety of techniques such as gravitational lensing, X-rays emission, Sunyaev-Zeldovich effect, dynamics of cluster galaxies, provides constraints on the nature of Dark Matter and on the behaviour of gravity on cosmological scales.

A successful exploitation of clusters as a cosmological tool heavily relies on understanding and characterizing the interplay between many astrophysical processes and on how such processes systematically bias our interpretation and modellization of the observables, as, e.g., biases in estimated masses. Within this line of research, we plan to take advantage of the different expertise present within different IFPU Institutes to develop a synergic effort for a definite assessment of clusters as cosmological probes.

The goal will be pursued by following three complementary main lines of investigation: 1. Exploitation of current multi-wavelength observational data to derive state-of-the-art cosmological constraints from already available cluster surveys; 2. Preparation to the cosmological exploitation of future cluster surveys (e.g. from Euclid, LSST, eROSITA, SPT-3G); 3. Theoretical/numerical description of galaxy clusters in order to assess systematics potentially limiting cluster cosmological applications (e.g. biases in mass measurements, calibration of survey selection functions, calibration of cosmic covariance).

We plan to develop these lines of research by organising regular (weekly) meetings at IFPU, and by proposing an intense program of events (e.g. meetings of the several collaborations in which team members are involved, workshop and invitation of high-profile experts in the field). The scientific activities will be advertised and monitored through a dedicated web page and disseminated through publications and presentations at international conferences.