The Kinematic Sunyaev-Zel'dovich Effect with Projected Fields II: prospects, challenges, and comparison with simulations

TL;DR

This paper evaluates the prospects and challenges of detecting the kinematic Sunyaev-Zel'dovich (kSZ) effect using a method that does not require individual redshift measurements, forecasting high signal-to-noise ratios with future CMB experiments.

Contribution

It introduces and assesses a redshift-independent cross-correlation method for measuring the kSZ effect, comparing its potential performance with simulations and forecasting results for upcoming experiments.

Findings

Forecasted high S/N ratios for future CMB experiments using the method.

Demonstrated the method's viability without individual redshift data.

Compared results with previous measurements using Planck and WMAP data.

Abstract

The kinematic Sunyaev-Zel'dovich (kSZ) signal is a powerful probe of the cosmic baryon distribution. The kSZ signal is proportional to the integrated free electron momentum rather than the electron pressure (which sources the thermal SZ signal). Since velocities should be unbiased on large scales, the kSZ signal is an unbiased tracer of the large-scale electron distribution, and thus can be used to detect the "missing baryon" that evade most observational techniques. While most current methods for kSZ extraction rely on the availability of very accurate redshifts, we revisit a method that allows measurements even in the absence of redshift information for individual objects. It involves cross-correlating the square of an appropriately filtered cosmic microwave background (CMB) temperature map with a projected density map constructed from a sample of large-scale structure tracers. We show that this method will achieve high signal-to-noise when applied to the next generation of high-resolution CMB experiments, provided that component separation is sufficiently effective at removing foreground contamination. Considering statistical errors only, we forecast that this estimator can yield $S/N \approx $ 3, 120 and over 150 for Planck, Advanced ACTPol, and hypothetical Stage-IV CMB experiments, respectively, in combination with a galaxy catalog from WISE, and about 20% larger $S/N$ for a galaxy catalog from the proposed SPHEREx experiment. This work serves as a companion paper to the first kSZ measurement with this method, where we used CMB temperature maps constructed from Planck and WMAP data, together with galaxies from the WISE survey, to obtain a 3.8 - 4.5$\sigma$ detection of the kSZ$^2$ amplitude.