The dark flow induced small scale kinetic Sunyaev Zel'dovich effect

Abstract

Recently Kashlinsky et al. 2008, 2010 reported a discovery of a $\sim 10^3$ km/$s$ bulk flow of the universe out to $z\simeq 0.3$, through the dark flow induced CMB dipole in directions of clusters. We point out that, if this dark flow exists, it will also induce observable CMB temperature fluctuations at multipole $\ell\sim 10^3$, through modulation of the inhomogeneous electron distribution on the uniform dark flow. The induced small scale kinetic Sunyaev Zel'dovich (SZ) effect will reach $\sim 1\muk^2$ at multipole $10^3\la \ell\la 10^4$, only a factor of $\sim 2$ smaller than the conventional kinetic SZ effect. Furthermore, it will be correlated with the large scale structure (LSS) and its correlation with 2MASS galaxy distribution reaches $0.3 \mu$K at $\ell=10^3$, under a directional dependent optimal weighting scheme. We estimate that, WMAP plus 2MASS should already be able to detect this dark flow induced small scale kinetic SZ effect with $\sim 6\sigma$ confidence. Deeper galaxy surveys such as SDSS can further improve the measurement. Planck plus existing galaxy surveys can reach $\ga 14\sigma$ detection. Existing CMB-LSS cross correlation measurements shall be reanalyzed to test the existence of the dark flow and, if it exists, shall be used to eliminate possible bias on the integrated Sachs-Wolfe effect measurement through the CMB-LSS cross correlation.