Clusters and Proto-clusters at z>1.5

Models predict that clusters of galaxies assemble from mergers of galaxy groups at z>1.5-2. The detections and observation of clusters and proto-clusters at these epochs put strong constraints on galaxy formation and quenching, and on the cosmological model.

Large-scale cosmological surveys in the next decade will detect thousands of these clusters and proto-clusters, through combined Euclid, Roman and LSST observations.  At present, hundreds of candidates are known, and our team has used space observations from HST and Spitzer to find quenched galaxies and merger signatures in ~20 spectroscopically confirmed clusters and proto-clusters from the CARLA survey, which consisted in Spitzer selected galaxy over-densities around radio loud AGN.

This thesis subject builds on our expertise from CARLA and current available space observations over the COSMOS and CANDELS fields.  The thesis supervisor is Co-I of two Spitzer legacy surveys,  the Euclid/WFIRST Spitzer Legacy Survey  ( and the Spitzer Euclid Deep Field South legacy survey.
The PhD student will find Spitzer-selected galaxy over-densities in these two surveys as cluster and proto-cluster candidates at z>1.5. S/he will build multi-wavelength space- and ground-based observation catalogs to identify the most probable candidates using  public HST and JWST observations of these fields, and follow them up with dedicated space- and ground-based programs. S/he will extend this search to future LSST fields. The results will be a catalog of new candidates and confirmed clusters and proto-clusters at z>1.5, and Spitzer-selected galaxy over-density maps to prepare future Euclid and LSST observations and analysis. Our results will be compared to our CARLA and other present survey observations to understand the limits and advantages of different survey selections, and to simulations to identify constrains on the cosmological model for the detection of the first large structures. Our results will be published in refereed papers, and the catalog and maps will be shared within the Rubin and Euclid collaborations.

The two Spitzer legacy surveys are collaborations with French, European and American colleagues. During the thesis, the student will have the opportunity to travel to the collaboration meetings and present her/his results to international conferences.


Simona Mei






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