The pairwise and cross-pairwise y-type polarised kinetic Sunyaev Zeldovich effect from transverse velocity of galaxy clusters

TL;DR

This paper introduces a new theoretical framework for detecting the polarised kinetic Sunyaev-Zeldovich effect caused by galaxy cluster transverse velocities, which can reveal insights into large-scale cosmic structure.

Contribution

The paper develops a novel theoretical approach and estimators for the pairwise and cross-pairwise polarised kSZ effect, enhancing prospects for detection with upcoming surveys.

Findings

Cross-pairing clusters with galaxies enables detection of the pkSZ effect with CMB-S4.

The pkSZ effect's spectrum is distinct, aiding its detectability independent of primary CMB anisotropies.

Large galaxy surveys can significantly improve the measurement of the pkSZ effect.

Abstract

We develop a new theoretical framework for studying the pairwise and cross-pairwise polarised kinetic Sunyaev Zeldovich (pkSZ) effect arising from the transverse peculiar velocity of galaxy clusters. The pkSZ effect is second order in peculiar velocities and has a spectrum that can be decomposed into y-type and blackbody components, whereas the unpolarised linear kSZ effect has only the blackbody component. Thus, the detectability of the pkSZ effect depends only on the sensitivity and the number of frequency channels of the survey and not on the other primary and secondary CMB anisotropies. We consider pairing of clusters with other clusters as well as cross-pairing of clusters with galaxies from spectroscopic galaxy surveys. The pairwise pkSZ signal is a function of intra-pair spatial separation. We develop and compare estimators of the pairwise pkSZ effect and study the detectability of the pairwise signal with cluster catalogs consisting of a few hundred thousand clusters expected from surveys such as eROSITA and CMB-S4. We find that cross-pairing clusters with galaxies from a large overlapping spectroscopic survey having a few billion galaxies will enable us to detect the pairwise pkSZ effect with CMB-S4. The pairwise pkSZ effect will thus open up a new window into the large-scale structure of the Universe in the coming decades.