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

Abstract

Abstract Recently, Kashlinsky et al. reported a discovery of a ∼103 km s−1 bulk flow of the Universe out to z≃ 0.3, through the dark flow induced cosmic microwave background (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 ℓ∼ 103, through modulation of the inhomogeneous electron distribution on the uniform dark flow. The induced small-scale kinetic Sunyaev–Zel'dovich (SZ) effect will reach ∼ 1 μ K2 at multipole 103≲ℓ≲ 104, only a factor of ∼ 2 smaller than the conventional kinetic SZ effect. Furthermore, it will be correlated with the large-scale structure (LSS) and its correlation with Two-Micron All-Sky Survey (2MASS) galaxy distribution reaches 0.3 μK at ℓ= 103, under a directional dependent optimal weighting scheme. We estimate that, Wilkinson Microwave Anisotropy Probe plus 2MASS should already be able to detect this dark flow induced small-scale kinetic SZ effect with ∼ 6σ confidence. Deeper galaxy surveys such as the Sloan Digital Sky Survey can further improve the measurement. Planck plus existing galaxy surveys can reach >rsim 14σ detection. Existing CMB–LSS cross-correlation measurements shall be reanalysed 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.