Université de GenèveDépartement de Physique ThéoriqueCAP Genève

Local Primordial Non-Gaussianities and Super-Sample Variance

1. June 2020
Cite as: 
Emanuele Castorina and Azadeh Moradinezhad Dizgah [arXiv: 2005.14677]
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Fluctuations with wavelengths larger than the volume of a galaxy survey affect the measurement of the galaxy power spectrum within the survey itself. In the presence of local Primordial Non-Gaussianities (PNG), in addition to the super-sample matter density and tidal fluctuations, the large-scale gravitational potential also induces a modulation of the observed power spectrum. In this work we investigate this modulation by computing for the first time the response of the redshift-space galaxy power spectrum to the presence of a long wavelength gravitational potential, fully accounting for the stochastic contributions. For biased tracers new response functions arise due to couplings between the small-scale fluctuations in the density, velocity and gravitational fields, the latter through scale dependent bias operators, and the large-scale gravitational potential. We study the impact of the super-sample modes on the measurement of the amplitude of the primordial bispectrum of the local-shape, f_{\rm NL}^{\rm loc}, accounting for modulations of both the signal and the covariance of the galaxy power spectrum by the long modes. Considering DESI-like survey specifications, we show that in most cases super-sample modes cause little or no degradation of the constraints, and could actually reduce the errorbars on f_{\rm NL}^{\rm loc} by (10 - 30)\%, if external information on the bias parameters is available.


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Université de Genève
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