Exploring Galaxy Clusters with the Atacama Cosmology Telescope

Abstract

Galaxy clusters are the largest known gravitationally bound structures in the Universe. Their abundance as a function of redshift and mass is very sensitive to the matter power spectrum and, hence, constitutes an essential probe for testing models of the Universe and constraining the rate of growth of cosmological structure. In this work we analyze the ACT S18dn cluster catalog of $2,869$ clusters detected via the Sunyaev-Zel’dovich effect. Specifically, we study the properties of the radial profiles extracted from the thermal map and test the predictions of two theoretical models for the cluster pressure profile, namely the Isothermal $\beta$ model and the Universal Pressure Profile (UPP). We also look at the profiles on the polarization maps to investigate whether or not there is a net polarization signal coming from the clusters. For both of these analysis, we use a stacking method, thoroughly described in Chapter \ref{ch:3}, which allows us to compute the average profiles at a specific mass and redshift by stacking over mass and redshift ranges at a very high level of precision with error bars at each radial bin $\sigma_r\lesssim 1\mu\mathrm{K}$. We then repeat the same analysis for the 525 clusters detected by the PlanckSZ2 survey \cite{planckSZ2} that are in the overlapping region with the ACT field map but were not detected by the ACT experiment. We found that by applying this stacking procedure we are able to resolve these clusters from the unfiltered ACT map and note some distinct features in the thermal profiles of these clusters when compared to those from the original ACT S18dn catalog.