The environment-dependence of the growth of the most massive objects in the Universe

TL;DR

This study uses the Simsilun simulation based on the silent universe approximation to show that relativistic effects and environment dependence influence the growth and mass distribution of the universe's most massive objects, exceeding predictions from standard models.

Contribution

It demonstrates that nonlinear relativistic effects cause environment-dependent variations in the growth of massive cosmic structures, differing from standard background-dependent approaches.

Findings

Mass function from Simsilun has higher amplitude at high masses.

Expected mass of the most massive objects is larger in Simsilun than in Tinker.

Relativistic effects influence the growth rate of the most massive clusters.

Abstract

This paper investigates the growth of the most massive cosmological objects. We utilize the Simsilun simulation, which is based on the approximation of the silent universe. In the limit of spatial homogeneity and isotropy the silent universes reduce to the standard FLRW models. We show that within the approximation of the silent universe the formation of the most massive cosmological objects differs from the standard background-dependent approaches. For objects with masses above $10^{15} M_\odot$ the effect of spatial curvature (overdense regions are characterized by positive spatial curvature) leads to measurable effects. The effect is analogous to the effect that the background cosmological model has on the formation of these objects (i.e. the higher matter density and spatial curvature the faster the growth of cosmic structures). We measure this by the means of the mass function and show that the mass function obtained from the Simsilun simulation has a higher amplitude at the high-mass end compared to standard mass function such as the Press-Schechter or the Tinker mass function. For comparison, we find that the expected mass of most massive objects using the Tinker mass function is $4.4^{+0.8}_{-0.6} \, \times 10^{15} M_\odot$, whereas for the Simsilun simulation is $6.3^{+1.0}_{-0.8} \, \times 10^{15} M_\odot$. We conclude that the nonlinear relativistic effects could affect the formation of the most massive cosmological objects, leading to a relativistic environment-dependence of the growth rate of the most massive clusters.