The kSZ optical depth degeneracy and future constraints on local primordial non-Gaussianity

TL;DR

This paper investigates how the overestimation of galaxy-electron cross correlation affects constraints on primordial non-Gaussianity from kSZ tomography, highlighting the importance of accurate modeling for future cosmological measurements.

Contribution

It analyzes the impact of galaxy-electron cross spectrum assumptions on primordial non-Gaussianity constraints using kSZ tomography, emphasizing the need for precise modeling.

Findings

Overestimation of galaxy-electron power affects non-Gaussianity constraints.

Future kSZ measurements can improve constraints under standard assumptions.

Suppressed galaxy-electron power at high redshift reduces the expected improvement.

Abstract

Recent reconstructions of the large-scale cosmological velocity field with kinetic Sunyaev Zeldovich (kSZ) tomography have returned an amplitude that is low with respect to the halo model prediction, captured by the kSZ velocity reconstruction bias $b_v <1$. This suggests that common choices for modeling the galaxy-electron cross correlation have systematically overestimated the true power, at least over scales and redshifts used in the velocity reconstruction measurements. In this paper, we study the implications of this overestimation for constraints on local-type primordial non-Gaussianity in current and near-future cosmological surveys. For concreteness, we focus on kSZ velocity reconstruction from a Vera Rubin Observatory-like survey in tandem with contemporary cosmic microwave background measurements. Assuming standard choices for the fiducial model of the small-scale galaxy-electron cross correlation, we find that upcoming kSZ tomography measurements can significantly improve constraints on local primordial non-Gaussianity via measurement of scale-dependent galaxy bias, in broad concordance with previous studies of the application of kSZ tomography to primordial non-Gaussianity. However, when we instead modify the assumed galaxy-electron cross-spectrum to be consistent with recent measurements of the velocity reconstruction bias, this picture can change appreciably. Specifically, we find that if the inferred suppression of galaxy-electron power persists at higher redshifts $z\gtrsim 1$, kSZ-driven improvement in local primordial non-Gaussianity constraints may be less significant than previously estimated. We explore how these conclusions depend on various modeling and experimental assumptions and discuss implications for the emerging program of kSZ velocity reconstruction.