Cross-Correlation of Planck CMB Lensing with DESI-Like LRGs

TL;DR

This paper reports a high-significance detection of cross-correlation between CMB lensing maps from Planck and DESI-like luminous red galaxies, providing insights into dark matter growth and galaxy bias at redshift 0.68.

Contribution

It presents the first precise measurement of CMB lensing and galaxy cross-correlation using DESI-like LRGs, including bias modeling and magnification bias correction.

Findings

Detected cross-correlation with S/N=27.2

Measured galaxy bias at z≈0.68 consistent with expectations

Quantified magnification bias corrections of a few percent

Abstract

Cross-correlations between the lensing of the cosmic microwave background (CMB) and other tracers of large-scale structure provide a unique way to reconstruct the growth of dark matter, break degeneracies between cosmology and galaxy physics, and test theories of modified gravity. We detect a cross-correlation between DESI-like luminous red galaxies (LRGs) selected from DECaLS imaging and CMB lensing maps reconstructed with the Planck satellite at a significance of $S/N = 27.2$ over scales $\ell_{\rm min} = 30$, $\ell_{\rm max} = 1000$. To correct for magnification bias, we determine the slope of the LRG cumulative magnitude function at the faint limit as $s = 0.999 \pm 0.015$, and find corresponding corrections on the order of a few percent for $C^{\kappa g}_{\ell}, C^{gg}_{\ell}$ across the scales of interest. We fit the large-scale galaxy bias at the effective redshift of the cross-correlation $z_{\rm eff} \approx 0.68$ using two different bias evolution agnostic models: a HaloFit times linear bias model where the bias evolution is folded into the clustering-based estimation of the redshift kernel, and a Lagrangian perturbation theory model of the clustering evaluated at $z_{\rm eff}$. We also determine the error on the bias from uncertainty in the redshift distribution; within this error, the two methods show excellent agreement with each other and with DESI survey expectations.