Kinetic Sunyaev-Zel'dovich effect and cosmic microwave background polarization from subsonic bulk motions of dense gas clouds in galaxy cluster cores

Recent Chandra observations have revealed the presence of cold fronts in many clusters of galaxies. The cold fronts are believed to be produced by the bulk motions of massive, dense, cold gas clouds with respect to the hotter, more rarefied ambient gas at velocities that can be as high as the speed of sound. This phenomenon may produce a significant contamination of both the kinetic Sunyaev-Zel'dovich (SZ) effect and the cosmic microwave background (CMB) polarization pattern observed in the direction of a cluster. We estimate the contributions to the kinetic SZ effect and to the CMB polarization toward galaxy clusters produced by the bulk motions of the gas in the inner parts of galaxy clusters. The observed cold fronts probe the absolute velocities of the gas motion, while the induced polarization and the kinetic SZ effect probe the transverse and the radial components, respectively. We show that these signals may be easily detected with sensitive future experiments, opening an exciting new window for studies of galaxy cluster internal dynamics and eventually facilitating reconstruction of the intrinsic cluster polarization of the CMB and the associated measure of the local CMB quadrupole.