Velocity Reconstruction from KSZ: Measuring $f_{NL}$ with ACT and DESILS

TL;DR

This paper reconstructs the large-scale cosmic velocity field using the kSZ effect with ACT and DESILS data, and constrains primordial non-Gaussianity, achieving the most stringent kSZ-based $f_{NL}$ limits to date.

Contribution

First 3D velocity reconstruction from kSZ effect using photometric galaxy survey data, and new tight constraints on local primordial non-Gaussianity.

Findings

Detected 11.7σ correlation between velocity field and galaxy survey.

Measured $f_{NL} = -39^{+40}_{-33}$, the most stringent kSZ-based constraint.

Observed low amplitude of kSZ correlation consistent with feedback models.

Abstract

The kinetic Sunyaev-Zel'dovich (kSZ) effect offers an indirect way to reconstruct large-scale cosmic velocities, by correlating high-resolution CMB temperature maps with galaxy surveys. In this work, we present the first three-dimensional reconstruction of the large-scale velocity field using a photometric galaxy survey, using data from the DESI Legacy Imaging Surveys (DESILS) and the Atacama Cosmology Telescope (ACT) DR5. We detect an $11.7\sigma$ correlation between our velocity reconstruction and the galaxy field, using only DESILS LRGs in the northern Galactic hemisphere. We find that the overall amplitude of the kSZ-induced correlation is low relative to a halo model prediction ($b_v = 0.45^{+0.06}_{-0.05}$), in agreement with previous results which find high feedback and smoothed gas profiles near massive galaxies. We use this measurement to place new constraints on local-type primordial non-Gaussianity (PNG), obtaining $f_{\rm NL}\!=\!-39^{+40}_{-33}$. This represents the most stringent $f_{\rm NL}$ constraint from kSZ velocity-based analyses to date. We validate our findings through extensive null tests, including tests for CMB foregrounds based on comparing 90 and 150 GHz CMB data.