The kinetic Sunyaev-Zel'dovich effect from the diffuse gas in the Local Group

Abstract

Since the Local Group (LG) of galaxies moves with a bulk velocity with respect to the cosmic microwave background radiation (CMB), free electrons in its gaseous halo should imprint large-scale non-primordial temperature shifts in the CMB via the kinetic Sunyaev-Zel'dovich (kSZ) effect. By modeling the distribution of gas in the LG halo and using its inferred velocity with respect to the CMB, we calculate the resulting kSZ signal from the diffuse LG medium. We find that it is dominated by a hot spot $\sim 10^\circ$ in size in the direction of M31, where the optical depth of free electrons is the greatest. By performing a correlation analysis, we find no statistical evidence that the kSZ signal from model of the LG halo is embedded in the CMB temperature map measured by the Planck satellite. We constrain the amount of mass in the LG halo by limiting the kSZ temperature shift around the hot spot to be smaller than the observed temperature shift in the Planck map. We find the tightest constraints for models where the halo mass is highly concentrated, with the mass limited to roughly $2.5-5\times 10^{12}$M$_\odot$, but note that halos with such high concentrations are rare.