Kinetic Sunyaev-Zel'dovich tomography with spectroscopic redshift: Surveys

Abstract

The kinetic Sunyaev-Zel'dovich (kSZ) effect is potentially a powerful tool that can be used to search for missing baryons. However, the kSZ signal is overwhelmed by various contaminations and the cosmological application is hampered by the loss of redshift information as a result of the projection effect. We propose a kSZ tomography method to alleviate these problems, with the aid of galaxy spectroscopic redshift surveys. We propose to estimate the large-scale peculiar velocity through the three-dimensional (3D) galaxy distribution, to weigh it using the 3D galaxy density and to adopt the product projected along the line of sight with a proper weighting as an estimator of the true kSZ temperature fluctuation Θ. Because the underlying directional dependence in the estimator Θ̂ closely resembles that in the true kSZ signal Θ, Θ̂ is tightly correlated with Θ. Thus, it avoids the problem of null correlation between the galaxy density and Θ, which prohibits the kSZ extraction through the usual density-cosmic microwave background (CMB) two-point cross-correlation measurement. Thus, we propose to measure the kSZ signal through the Θ̂-Θ cross-correlation. This approach has a number of advantages. (i) Because of the underlying directional dependence of Θ̂, it is uncorrelated with the primary CMB, the thermal SZ effect and astrophysical contaminations, such as dusty star-forming galaxies. Thus, the Θ̂-Θ cross-correlation picks up the kSZ signal in the SZ survey in a clean manner. (ii) With the aid of galaxy redshifts, the cross-correlation recovers the redshift information of the kSZ signal and allows for a more detailed investigation of missing baryons. (iii) As galaxy surveys usually have a high signal-to-noise (S/N) ratio, the S/N ratio of the kSZ measurement through the Θ̂-Θ cross-correlation can be significantly improved. We test the proposed kSZ tomography against non-adiabatic and adiabatic hydrodynamical simulations.We confirm that Θ̂ is indeed tightly correlated with Θ at k ≲ 1 h Mpc-1, although non-linearities in the density and velocity fields and non-linear redshift distortion do weaken the tightness of the Θ̂-Θ correlation. We further quantify the reconstruction noise in Θ̂ from galaxy distribution shot noise. Based on these results, we quantify the applicability of the proposed kSZ tomography for future surveys.We find that, in combination with the BigBOSSN spectroscopic redshift survey, the Planck CMB experiment will be able to detect the kSZ effect with an overall significance of ~50σ and further measure its redshift distribution at many redshift bins over 0 < z < 2. © 2011 The Authors. Monthly Notices of the Royal Astronomical Society © 2011 RAS.