Research

I am mainly interested in galaxy clusters and their use in cosmology.

Background: Cosmology with galaxy clusters

My research activity lies in the field of observational cosmology, in particular using galaxy clusters as a cosmological probe. Hosted by the most massive dark matter halos in the Universe, galaxy clusters represent a formidable tracer of the cosmic matter distribution, and of its evolution with time. Their distribution in mass and redshift is therefore tightly linked to the evolution of the Universe, allowing large cluster surveys to be used to set constraints on cosmological parameters.

I am particularly interested in cluster surveys built from millimeter-wave datasets. At these wavelengths, galaxy clusters can be detected via their imprint on the cosmic microwave background (CMB) through the thermal Sunyaev-Zeldovich (tSZ) effect, which is the spectral distortion of the CMB due to the Compton scattering of its photons on the free electrons of the hot intracluster medium (ICM) plasma. As a spectral distortion of the CMB, the tSZ signal is redshift-independent, enabling the detection of distant clusters, and thus the construction of catalogs spanning large redshift ranges. The tSZ effect has been successfully used to build large catalogs of thousands of galaxy clusters up to high redshifts, using surveys such as Planck, the Atacama Cosmology Telescope (ACT), and the South Pole Telescope (SPT). An additional advantage of the tSZ effect for cluster cosmology is its ability to provide precise relative mass calibration of cluster samples. Since the theoretical prediction from cosmology is the abundance of clusters in mass and redshift, the cosmological exploitation of a cluster sample requires estimates of cluster masses. Mass calibration is one of the main bottlenecks of cluster cosmology, since it is both challenging (as the measurement of cluster masses can be difficult) and crucial (as its accuracy and precision directly impact those of the inferred cosmological constraints). To tackle this issue, tSZ-selected samples are particularly useful, as the amplitude of the tSZ effect tightly correlates with cluster mass. Hence, by determining the masses of only a subset of clusters, one can calibrate a statistical relationship between mass and tSZ signal, and use it to derive precise constraints on cluster masses from their tSZ signal.