Dynamics of Nearby Groups of Galaxies: the role of the cosmological constant

TL;DR

This study investigates how a cosmological constant influences the dynamics of nearby galaxy groups by modifying the Lemaître-Tolman model and fitting it to observational data, finding that current data cannot conclusively detect its effects.

Contribution

The paper introduces a modified Lemaître-Tolman model including the cosmological constant and applies it to galaxy group data to estimate masses and the Hubble constant.

Findings

Velocity-distance relations fit data equally well with or without the cosmological constant.

Estimated Hubble constant is 65±7 km/s/Mpc from local flow data.

No definitive evidence of the cosmological constant's effect on galaxy group dynamics.

Abstract

(context) Different cosmological data are consistent with an accelerated expansion produced by an exotic matter-energy component, dubbed "dark-energy''. A cosmological constant is a possibility since it satisfies most of the observational constraints. (aims) In this work, the consequences of such a component in the dynamics of groups of galaxies is investigated, aiming to detect possible effects in scales of the order of few Mpc. (methods) The Lema\^itre-Tolman model was modified by the inclusion of the cosmological constant term and, from the numerical solution of the equations of motion, a velocity-distance relation was obtained. This relation depends on two parameters: the central core mass and the Hubble parameter. The non-linear fit of such a relation to available data permitted to obtain masses for five nearby groups of galaxies and for the Virgo cluster as well as estimates of the Hubble constant. (results) The analysis of the present results indicates that the velocity-distance relation derived from the modified Lema\^itre-Tolman model as well as that derived from the "canonical'' model give equally acceptable fits to the existent data. As a consequence, any robust conclusion on the effects of the cosmological constant in the dynamics of groups could be established. The mean value of the Hubble parameter derived from the present study of local flows is H_0 = 65\pm 7 km/s/Mpc.