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Biases in the estimation of galaxy clusters dynamical mass


  • Mr. Antonio FERRAGAMO

Auteurs principaux



The abundance of galaxy clusters, per unit of mass and redshift, is a very powerful tool in order to constrain cosmological parameters as the matter density Ωm, and the amplitude of the primordial fluctuation σ8. However, the cluster mass is not an observable. The multicomponent nature of galaxy clusters helps to bypass this problem. In fact, from the observation of each different cluster component, it is possible to measure quantities that are directly correlated with the total mass of the cluster. These quantities are known as mass proxies. Spectroscopic observations in optical and infrared wavelengths allow to measure the redshift of cluster members and so obtain their velocity dispersion, which is an estimate of how galaxies are moving into the cluster potential well. Therefore, under the assumption of dynamical equilibrium, the virial theorem correlates the velocity dispersion with the total cluster mass. However, as all mass proxies, the velocity dispersion suffers from biases that have to be corrected in order to obtain an unbiased cluster mass. By using hydrodynamical simulations, we have studied statistical and physical effects induced by the choice of a particular dispersion estimator and other effects such as the reduced number of cluster members considered the interlopers contamination and the projected radius in which the clusters members are sampled. The result of this study is a series of corrections in order to obtain a bias-corrected velocity dispersion and therefore, a bias-corrected cluster mass. As a test example, I will discuss the application of this methodology to our follow-up effort for characterizing the Planck PSZ1 sample in the northern sky.