The Hubble diagram for a system within dark energy: influence of some relevant quantities

Abstract

Aims. We study the influence of relevant quantities, including the density of dark energy (DE), to the predicted Hubble outflow around a system of galaxies. In particular, we are interested in the difference between two models: 1) the standard ΛCDM model, with the everywhere constant DE density, and 2) the "Swiss cheese model", where the Universe is as old as the standard model and the DE density is zero on short scales, including the environment of the system. Methods. We calculated the current predicted outflow patterns of dwarf galaxies around the Local Group-like system, using different values for the mass of the group, the local DE density, and the time of ejection of the dwarf galaxies, which are treated as test particles. These results are compared with the observed Hubble flow around the Local Group. Results. The predicted distance-velocity relations around galaxy groups are not very sensitive indicators of the DE density, owing to the observational scatter and the uncertainties caused by the mass used for the group and a range in the ejection times. In general, the Local Group outflow data agree with the local DE density being equal to the global one, if the Local Group mass is about 4 × 10 12 M ; a lower mass < ∼ 2×1012 M could suggest a zero local DE density. The dependence of the inferred DE density on the mass is a handicap in this and other common dynamical methods. This emphasizes the need to use different approaches together, for constraining the local DE density.

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

“…by Lynden-Bell (1981). In addition, the effect of Λ increases R ZV by about 1.15, or the inferred mass by about 1.5 (Peirani & de Freitas Pacheco 2006;Saarinen & Teerikorpi 2014;Tully 2015). The calculation leads to log ρM ρΛ ≈ 0.75.…”

“…For a recent study about the DE in the vicinity of the Local Group see Saarinen & Teerikorpi (2014). 1 The difference from the previous WMAP value (≈7×10 −30 g cm −3 ) is mainly caused by the smaller value of the Hubble constant (h = 0.67), lowering the critical density (1.88h 2 × 10 −30 g cm −3 ) which is now equal to ρ crit = 8.52 × 10 −30 g cm −3 .…”

“…1 Because of the non-uniform distribution of gravitating matter, the cosmic antigravity can be stronger than gravity also locally on scales of ∼ 1−10 Mpc (Chernin 2001), which in principle makes it possible to detect the DE in the local galaxy universe, as reviewed by Byrd et al (2012Byrd et al ( , 2015. For a recent study about the DE in the vicinity of the Local Group, see Saarinen & Teerikorpi (2014).…”

Total mass beyond r200 for systems with different density profile laws within a Λ background

“…The effect of Λ increases R 0 by about 1.15 (e.g., Peirani & de Freitas Pacheco ; Saarinen & Teerikorpi ).…”