The skewness of z=0.5 redshift-space galaxy distribution in Modified Gravity

TL;DR

This study investigates the skewness of galaxy distributions at redshift 0.5 in modified gravity models using mock catalogues, revealing potential for distinguishing these models from standard cosmology through galaxy data analysis.

Contribution

It is the first to analyze the third reduced moment of galaxy distributions in redshift space for modified gravity models using realistic mock catalogues.

Findings

Modified gravity models cause 2-3% deviations in skewness compared to ΛCDM.

The skewness signal persists in realistic galaxy samples, enabling potential model discrimination.

Higher density galaxy samples can improve constraints by reducing shot-noise effects.

Abstract

We study the reduced skewness, $S_{3,g}\equiv\bar{\xi}_{3,g}/\bar{\xi}_{2,g}^2$ of galaxy distribution at $z=0.5$ in two families of modfied gravity models: the Hu-Sawicki $f(R)$-gravity and normal-branch of Dvali-Gabadadze-Porrati (nDGP) models. We use a set of mock galaxy catalogues specifally designed to match CMASS spectroscopic galaxy sample. For the first time we investigate the third reduced moment of such galaxy distributions both in the redshift space. Our analysis confirms that the signal previously indicated only for dark matter halo catalogues persists also in realistic mock galaxy samples. This result offers a possibility to extract a potential modified gravity signal in $S_3$ from spectroscopic galaxy data without a need for a very precise and self-consistent RSD models constructed for each and every modified gravity scenario separately. We show that the relative deviations from $\Lambda$CDM~ $S_{3,g}$ of various modified gravity models can vary from $7$ down to $\sim 2-3\%$ effects. Albeit, the effect looks small, we show that for considered models it can foster a $2-3\sigma$ falsification. Finally we argue that galaxy sample of a significantly higher number density should provide even stronger constraints by limiting shot-noise effects affecting the $S_{3,g}$ estimates at small comoving separations.