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

TL;DR

This paper predicts a small scale kinetic Sunyaev-Zel'dovich effect caused by the dark flow, which can be detected through CMB and galaxy survey correlations, providing a new way to test the dark flow hypothesis.

Contribution

It introduces the concept of a small scale kinetic SZ effect induced by dark flow and proposes methods for its detection using existing and future surveys.

Findings

Dark flow induces observable small scale CMB fluctuations.

The effect correlates with large scale structure and can be detected at high significance.

Reanalysis of existing data can test the dark flow hypothesis.

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.