Estimation and mitigation of foregrounds in projected kSZ velocity reconstruction

TL;DR

This paper analyzes foreground biases in kSZ velocity reconstruction, introduces a parity-odd estimator to cancel contamination, and demonstrates its effectiveness with ACT and DESI data, achieving an 11σ detection.

Contribution

It develops a new parity-odd estimator that cancels foreground contamination in kSZ velocity measurements without losing cosmological information.

Findings

Foreground biases from tSZ and CIB are modeled and compared with data.

The parity-odd estimator effectively cancels foreground contamination.

Application to ACT and DESI data yields an 11σ detection of the velocity-galaxy correlation.

Abstract

The kSZ effect has recently emerged as a powerful probe for precision cosmology through its ability to reconstruct the large-scale velocity field. In particular, the kSZ-reconstructed velocity-galaxy cross-correlation is sensitive to signatures of primordial non-Gaussianity through its imprint on the galaxy bias. The kSZ velocity reconstruction is performed using small-scale information from CMB temperature and galaxy overdensities. As the sensitivity of these measurements improves, systematic effects such as extragalactic foreground contamination present in CMB maps become increasingly important. We present a study of foreground biases to the kSZ-reconstructed velocity-galaxy cross-correlation. We derive the relevant foreground contributions from the thermal Sunyaev-Zel'dovich effect and the cosmic infrared background, modeling them using a halo model description of the dominant one- and two-halo terms. We compare our analytic predictions to measurements obtained using ACT DR6 temperature maps and DESI Legacy Imaging Survey galaxies, finding qualitative agreement. We introduce a parity-odd estimator constructed from antisymmetric combinations of tomographic velocity-galaxy correlations and show analytically that, under the Limber approximation, this estimator entirely cancels the foreground contamination while preserving the full cosmological signal without loss of signal-to-noise. Finally, we apply this parity-odd estimator to the data combination mentioned above and show that the fit to the velocity-galaxy correlation is dramatically improved compared to the analysis without mitigation; our estimator detects the signal at 11$\sigma$, with an amplitude consistent with recent studies.