Constrained simulations of the local universe: II. The nature of the local Hubble flow

TL;DR

This study uses N-body simulations across different CDM cosmologies to analyze the coldness of the local Hubble flow, finding it is unaffected by dark energy and mainly influenced by local galaxy distribution and isolation.

Contribution

It demonstrates that the coldness of the local Hubble flow is not due to dark energy and highlights the importance of local galaxy environment and isolation in this phenomenon.

Findings

The coldness of the Hubble flow is similar in \\LCDM and OCDM models.

The coldness is problematic for \\LCDM only if local density exceeds twice the cosmic mean.

Isolation of the Local Group influences the flow's coldness.

Abstract

Using a suite of N-body simulations in different Cold Dark Matter (CDM) scenarios, with cosmological constant (\LCDM) and without (OCDM, SCDM), we study the Hubble flow (\sigh) in Local Volumes (LV) around Local Group (LG) like objects found in these simulations, and compare the numerical results with the most recent observations. We show that \LCDM and OCDM models exhibit the same behavior of \sigh. Hence, we demonstrate that the observed coldness of the Hubble flow is not likely to be a manifestation of the dark energy, contrary to previous claims. The coldness does not constitute a problem by itself but it poses a problem to the standard \LCDM model only if the mean density within the Local Volume is greater than twice the mean matter cosmic density. The lack of blueshifted galaxies in the LV, outside of the LG can be considered as another manifestation of the coldness of the flow. Finally, we show that the main dynamical parameter that affects the coldness of the flow is the relative isolation of the LG, and the absence of nearby Milky Way like objects within a distance of about $3\mpc$.