Marcos Lima

Galaxy Clusters

Galaxy clusters are powerful probes of cosmology, since their abundance as a function of redshift and mass depends both on the expansion and growth of density fluctuations in the Universe. They are the largest objects in the Universe that have reached virial equilibrim (or not!), and can be observed in various frequencies, exposing different aspects of the physical processes happening inside the cluster constituents, such as galaxies and hot gas.

The main challenge in using clusters to constrain cosmology is that their masses are not observed directly and need to be inferred from mass proxies, such as their richness (number of galaxies), X-ray flux or temperature, SZ flux and their lensing shear. One needs to determine the relationship between mass and observables, including its redshift evolution, in order to use clusters for cosmology.

With Wayne Hu, I have studied self-calibration techniques, which allow one to solve simultaneously for parameters of the mass-observable relation, as well as for the cosmological parameters of interest. I have also investigated the requirements on redshift precision in order to use self-calibration methods. With Hiro Oyaizu, Fabian Schmidt and Wayne Hu, I have also looked at the effect of modified gravity theories on properties of galaxy clusters, such as their abundance and bias.