A graph of dark energy significance on different spatial and mass scales

TL;DR

This paper introduces a 'Lambda significance graph' to analyze the influence of dark energy versus matter across different cosmic structures, providing insights into their dynamical states and the transition between gravity and dark energy dominance.

Contribution

It presents a novel graphical method to compare matter and dark energy densities across scales, illustrating the dynamical regimes of galaxy systems within the Lambda CDM model.

Findings

Galaxy groups are generally in gravity-dominated regions.

Extended clusters and superclusters approach the dark energy dominance boundary.

The scale-mass relation intersects the balance line near the correlation length.

Abstract

The current cosmological paradigm sees the formation and evolution of the cosmic large-scale structure as governed by the gravitational attraction of the Dark Matter (DM) and the repulsion of the Dark Energy (DE). We characterize the relative importance of uniform and constant dark energy, as given by the Lambda term in the standard LCDM cosmology, in galaxy systems of different scales, from groups to superclusters. An instructive "Lambda significance graph" is introduced where the matter-DE density ratio <rho_M>/rho_Lambda for different galaxy systems is plotted against the radius R. This presents gravitation and DE dominated regions and shows directly the zero velocity radius, the zero-gravity radius, and the Einstein-Straus radius for any fixed value of mass. Example galaxy groups and clusters from the local universe illustrate the use of the Lambda significance graph. These are generally located deep in the gravity-dominated region <rho_M}>/rho_Lambda > 2, being virialized. Extended clusters and main bodies of superclusters can reach down near the border line between gravity-dominated and DE dominated regions <rho_M>/rho_Lambda = 2. The scale--mass relation from the standard 2-point correlation function intersects this balance line near the correlation lenght. The log <rho_M>/rho_Lambda vs. log R diagram is a useful and versatile way to characterize the dynamical state of systems of galaxies within the Lambda dominated expanding universe.