Dissecting Cluster Cosmology: toward a roadmap for forthcoming cluster surveys

Old SISSA Building - Room D

Old SISSA Building - Room D

Via Beirut, 2, 34151 Trieste TS Coffee Breaks and Reception will take place in the ICTP terrace, nearby the meeting venue.


In the last decade, astronomical data-sets have started to be widely and quantitatively used by the scientific community to address important physical questions such as: the nature of the dark matter and dark energy components and their evolution; the physical properties of the baryonic matter; the sum of neutrino masses; the nature of gravity at cosmological scales.

Most of these results are based on well-established geometrical cosmological probes (e.g. galaxies, supernovae, cosmic microwave background). Galaxy clusters provide a complementary and necessary approach, as their distribution as a function of time and observables is sensitive to both the geometrical and the dynamical evolution of the Universe, driven by the growth of structures.

Galaxy clusters trace in fact the extreme peaks in the matter density field on Mpc scales. The abundance of these peaks as a function of mass and redshift is highly sensitive to the matter density and the growth of structure and, under the assumption that their abundance can be accurately predicted for a given cosmology, the measurements of cluster abundance can yield powerful cosmological constraints.

Current cosmological constraints from galaxy clusters have demonstrated to provide a consistency test of the dark energy paradigm and the validity of general relativity (GR).
The ability to cleanly select clusters out to the redshift at which cosmic acceleration takes over is particularly important to disentangle between the dark energy paradigm and possible modifications of GR. Ideally, a cluster survey must be able to provide a sample of clusters which:

  • extends to high-redshift
  • presents a clean selection-function
  • has associated observables tightly connected to the cluster mass.


While the dominant systematics in current cluster cosmological studies is associated to the capability of accurate and precisely constrain the mass-observable relation for cluster samples, the extremely large statistics of samples widely extending both the mass and redshift range of upcoming cluster surveys (e.g., SPT-3G, eRosita, Euclid and LSST) will stress every single aspect associated to cluster cosmology.

In particular a careful and detailed characterization of all the relevant steps will be needed, including:

  • the identification of the cluster samples in multi-wavelength data-sets
  • the accurate characterization of the associated selection function
  • the accurate and precise process of calibration of the mass-observable relation
  • the accurate and precise calibration of the theoretical uncertainties associated to the halo-mass function and halo bias
  • the correct definition of the likelihood


This workshop aims at bringing together leading experts in all the above-mentioned relevant topics, from the very first steps of the definition of a cluster survey to the final cosmological posteriors, in order to define a path toward fully exploiting the overwhelming quantity and quality of data that will become available in the next decade from cosmological surveys at different wavelengths.

Proposed activities:

The meeting will take place in Trieste from the 3rd to the 7th of July 2023 at the institute for the Fundamental Physics of the Universe (IFPU; https://www.ifpu.it). The workshop will be organized in thematic discussions, each focusing on a specific topic that needs to be addressed to firmly establish clusters as credible cosmological tools in the era of large surveys. Each of such discussions will be opened by a limited number of talks (1-2 of about 30 mins each), followed by an open and frank discussion, that will be chaired by a participant expert of the specific topic of the discussion.

The ambitious goal of this workshop is to define a clear path towards the publication of a white paper which should present to the community current challenges and the required road map that will enable cluster cosmology with next generation cluster surveys. 


List of thematic discussions:

Cluster identification and selection function:

  • optical/near-IR photometry;
  • X-rays;
  • Sunyaev-Zeldovich effect.

Calibration of halo masses:

  • weak lensing;
  • dynamical methods;
  • hydrostatic equilibrium;
  • scaling relations and multi-wavelength mass calibration.

Likelihood definition:

  • likelihood for cluster number counts and clustering;
  • likelihood for the calibration of the observable-mass relation;
  • definition of (co-)variances.

Theoretical systematics:

  • calibration of the halo mass function;
  • calibration of the halo bias

calibration of cosmic (co-)variances.

We will (try to) stream talks here:


  • Alessandra Fumagalli
  • Alexandro Saro
  • Andrea Biviano
  • Andres Salcedo
  • Ang Liu
  • Anja von der Linden
  • Barbara Sartoris
  • Carlo Giocoli
  • Christian Labarbuta
  • Daisuke Nagai
  • Eduardo Rozo
  • Emiliano Munari
  • Facundo Rodriguez
  • Giorgio Lesci
  • Jean-Baptiste Melin
  • Keiichi Umetsu
  • Laura Salvati
  • Lorenzo Lovisari
  • Luca Di Mascolo
  • Mario Nonino
  • Marisa Girardi
  • Matteo Costanzi
  • Sebastian Grandis
  • Stefano Borgani
  • Stefano Ettori
  • Tiago Batalha De Castro
  • Tim Schrabback
  • Veronica Biffi
Organizers: Stefano Borgani, Tiago Batalha de Castro, Matteo Costanzi, Alexandro Saro