Constraints on primordial non-Gaussianity from Galaxy-CMB lensing cross-correlation

TL;DR

This paper proposes using the cross-correlation between CMB lensing and galaxy distribution to improve constraints on primordial non-Gaussianity, demonstrating that future surveys could significantly tighten these constraints especially with highly biased, high-redshift objects.

Contribution

It introduces a novel method of combining CMB lensing and galaxy data to better measure primordial non-Gaussianity, providing forecasts for upcoming surveys.

Findings

Wide field galaxy surveys outperform deep surveys in constraining f_NL.

Expected error on f_NL can be as low as 10-20 with current experiments.

Future surveys could achieve errors around 5 with high-redshift, biased objects.

Abstract

Recent studies have shown that the primordial non-Gaussianity affects clustering of dark matter halos through a scale-dependent bias and various constraints on the non-Gaussianity through this scale-dependent bias have been placed. Here we introduce the cross-correlation between the CMB lensing potential and the galaxy angular distribution to effectively extract information about the bias from the galaxy distribution. Then, we estimate the error of non-linear parameter, f_NL, for the on-going CMB experiments and galaxy surveys, such as Planck and Hyper Suprime-Cam (HSC). We found that for the constraint on f_NL with Planck and HSC, the wide field galaxy survey is preferable to the deep one, and the expected error on f_NL can be as small as: \Delta f_NL ~ 20 for b_0 = 2 and \Delta f_NL ~ 10 for b_0 = 4, where b_0 is the linear bias parameter. It is also found that future wide field galaxy survey could achieve \Delta f_NL ~ 5 with CMB prior from Planck if one could observe highly biased objects at higher redshift (z ~ 2).