Iskay2: Signal Extraction of the Kinematic Sunyaev-Zel'dovich Effect Through The Pairwise Estimator. Pipeline and Validation

TL;DR

The paper addresses extracting the small kinematic SZ (kSZ) pairwise signal by cross-correlating CMB maps with spectroscopic galaxy catalogs. It introduces iskay2, a Python pipeline built on Corrfunc that implements the pairwise kSZ estimator in a fast, scalable way. The authors validate iskay2 against ACT DR5 results and C21, demonstrating agreement within 1σ and a roughly 50× speed-up that enables bootstrapped covariance estimation for catalogs near $10^6$ tracers. They also provide a pathway for high-significance measurements with DESI and upcoming high-resolution CMB surveys (ACT DR6, SPT, Simons Observatory), which will tighten constraints on cosmic growth and gravity through the pairwise kSZ signal, with the estimator given by $\hat{p}(r) = - \frac{\sum c_{ij} dT_{ij}}{\sum c_{ij}^2}$ where $c_{ij} = \frac{1}{2} \hat{r}_{ij} \cdot (\hat{r}_i - \hat{r}_j)$ and $dT_{ij} = T_{AP}^i - T_{AP}^j$.

Abstract

The peculiar motions of massive halos probe the distribution of matter in the universe, the gravitational potential, and the history of cosmic structure growth. The kinematic Sunyaev-Zeldovich (kSZ) effect offers a robust observational window into these properties. The pairwise kSZ estimator probes the pairwise momentum of groups of galaxies by cross-correlating cosmic microwave background (CMB) maps with spectroscopic galaxy catalogs, using galaxies to trace the positions of dark matter halos. This note introduces iskay2, an efficient pipeline designed to apply the pairwise kSZ estimator to maps of the CMB and large galaxy catalogs. Pairwise kSZ measurements obtained using this pipeline are compared to previously published results and are shown to be consistent within statistical expectations. This pipeline will enable high-precision measurements of the pairwise kSZ utilizing galaxy catalogs like DESI combined with past, current and next-generation high-resolution CMB experiments such as ACT, SPT and the Simons Observatory.

Figures (1)

• Figure 1: Measured pairwise estimator using the full iskay2 pipeline on the ACT DR5 maps compared with published result in C21 showing agreement among the two pipelines. Differences among the mean values are lower than one sigma, and differences among the size of the bootstrapped error bars are consistent with random variance among the two runs. Iskay2 performs $\sim 50\times$ faster than Iskay1 (C21), enabling computation of bootstrapped pairwise kSZ curves using galaxy tracer catalogs of order 1 million tracers, such as DESI.