Constraints on Cosmology and Gravity from the Dynamics of Voids

TL;DR

This paper uses galaxy distributions around cosmic voids to measure key cosmological parameters, providing new constraints on matter density and structure growth, and testing gravity theories in low-density regions.

Contribution

It introduces a novel method leveraging void-galaxy correlations to constrain cosmology and gravity, improving on previous small-scale measurements with minimal assumptions.

Findings

Measured matter density $oxed{ ext{Ω}_ ext{m}=0.281 extpm0.031}$

Determined growth rate $f/b=0.417 extpm0.089$ at median redshift 0.57

Found no evidence for deviations from general relativity

Abstract

The Universe is mostly composed of large and relatively empty domains known as cosmic voids, whereas its matter content is predominantly distributed along their boundaries. The remaining material inside them, either dark or luminous matter, is attracted to these boundaries and causes voids to expand faster and to grow emptier over time. Using the distribution of galaxies centered on voids identified in the Sloan Digital Sky Survey and adopting minimal assumptions on the statistical motion of these galaxies, we constrain the average matter content $\Omega_\mathrm{m}=0.281\pm0.031$ in the Universe today, as well as the linear growth rate of structure $f/b=0.417\pm0.089$ at median redshift $\bar{z}=0.57$, where $b$ is the galaxy bias ($68\%$ C.L.). These values originate from a percent-level measurement of the anisotropic distortion in the void-galaxy cross-correlation function, $\varepsilon = 1.003\pm0.012$, and are robust to consistency tests with bootstraps of the data and simulated mock catalogs within an additional systematic uncertainty of half that size. They surpass (and are complementary to) existing constraints by unlocking cosmological information on smaller scales through an accurate model of nonlinear clustering and dynamics in void environments. As such, our analysis furnishes a powerful probe of deviations from Einstein's general relativity in the low-density regime which has largely remained untested so far. We find no evidence for such deviations in the data at hand.