Non-Gaussian halo bias and future galaxy surveys

TL;DR

This work analyzes how forthcoming galaxy surveys can constrain primordial non-Gaussianity by exploiting the scale-dependent halo bias induced by NG on large scales. Using the MV08 framework to connect NG in the primordial potential to halo clustering and combining large-scale power-spectrum shape with ISW cross-correlations, the authors forecast that constraints on $|f_{NL}|$ can reach unity for horizon-volume surveys. They also show that non-local and scale-dependent NG contributions can enhance the effective $f_{NL}$ for large-scale structure, making the LSS signal competitive with CMB bispectrum constraints. The results highlight the complementarity of galaxy-power and ISW probes and emphasize the importance of accounting for non-local NG shapes in future surveys.

Abstract

We forecast constraints on primordial non-Gaussianity achievable from forthcoming surveys by exploiting the scale-dependent halo bias introduced on large scales by non-Gaussian initial conditions. We explore the performance of exploiting both the shape of the galaxy power-spectrum on large scales and the cross-correlation of galaxies with Cosmic Microwave Background maps through the Integrated Sachs Wolfe effect. We find that future surveys can detect primordial non-Gaussianity of the local form with a non-Gaussianity parameter $|f_{\rm NL}|$ of order unity. This is particularly exciting because, while the simplest single-field slow-roll models of inflation predict a primordial $|f_{\rm NL}|\ll 1$, this signal sources extra contributions to the effective $f_{\rm NL}$ of large-scale structures that are expected to be above our predicted detection threshold.