Galaxy Clusters as mirrors of the distant Universe. Implications for the kSZ and ISW effects

Understand

It is well known that Thomson scattering of CMB photons in galaxy clusters introduces new anisotropies in the CMB radiation field, but however little attention is payed to the fraction of CMB photons that are scattered off the line of sight, causing a slight blurring of the CMB anisotropies present at the moment of scattering.

• In this work we study this {\it blurring} effect, and find that it has a non-negligible impact on estimations of the kinetic Sunyaev-Zel'dovich (kSZ) effect: it induces a 10% correction in 20-40% of the clusters/groups, and a 100% correction in $\sim 5$% of the clusters in an ideal (noiseless) experiment.
• We explore the possibility of using this blurring term to probe the CMB anisotropy field at different epochs in our Universe.
• In particular, we study the required precision in the removal of the kSZ that enables detecting the blurring term $-\tau_T \delta T / T_0$ in galaxy cluster populations placed at different redshift shells.