Line of research overview

Cosmology with Galaxy Clusters

Principal Investigator: Stefano Borgani

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.

Status of project and perspectives:

The project is being carried out along two main lines of investigation, which are tightly intertwined:

1. Astrophysics of galaxy clusters: comparison between observational data and numerical simulations.
2. Cosmological applications of galaxy clusters.

In the following, we provide a short description of the main activities carried out for each one of such two activities.

1. Advanced cosmological hydrodynamical simulations of galaxy clusters are carried out with the purpose of studying the main processes shaping the observational properties of galaxy clusters at different wavelengths and how they impact on the evolution of their different components: intra-cluster medium, cluster galaxies and distribution of the Dark Matter component. Predictions from cosmological hydrodynamical simulations are compared with observational data with the purpose of constraining models of galaxy formation in the extreme environment represented by clusters. Clearly, understanding galaxy clusters as astrophysical objects is instrumental also for their application as tools to follow cosmic evolution and, ultimately, to constrain cosmological parameters.
2. Most of the participants to this project are also active members of the Euclid Consortium (EC), in particular for the activities related to the cosmological exploitation of the cluster survey to be carried out by the ESA’s Euclid mission (launch expected in 2023). Within the EC, several members of this project also have coordination roles in several activities defining different steps bringing from the raw data analysis, to the identification of clusters, to the measurements of their mass scale, to the inference of cosmological constraints. As the launch of the Euclid satellite is approaching, we expect that such activities will represent the core of the research carried out at IFPU within this project for the next several years.

Since Spring 2020, our activities have been significantly affected by the COVID pandemic. The main consequence of this is that some of our activities have been carried out remotely, while others have been necessarily suspended. With the regression of the pandemic, more and more activities and informal meetings are again taking place in presence, while suspended activities are being rescheduled.

The most important regular activity is represented by our weekly Journal Club, which has smoothly and successfully continued by remote during the pandemic, and now is organized in a hybrid mode. This JC activity is organized by alternating critical discussions of papers from the arXiv, internal reports on ongoing projects and papers in which IFPU members are involved, and seminars on specific arguments from colleagues external to IFPU. Also within the activities of this JC, we organized in Spring 2021 a series of lectures on Machine Learning methods applied to astrophysics and cosmology. A total of nine lectures have been delivered by external experts in the field: Massimo Brescia, Ben Hoyle and Francisco Navarro Villaescusa Navarro. A IFPU workshop on “Dissecting Cluster Cosmology” originally approved for June 2020, was cancelled for the COVID outbreak, and lately held by remote in a reduced format on 1 of September 2020. The workshop is now officially rescheduled for 3-7 of July 2023. The main motivation of this workshop is to bring together a relatively small number (about 20) of colleagues, who will join IFPU members working on cluster cosmology, to address one by one the main issues concerning the cosmological application of galaxy clusters.