New study shed light on the nature of mysterious dark energy

A team of cosmologists compared the theoretical predictions of the maximal abundance of massive galaxies predicted in different dynamical dark energy (DDE) models at high redshifts z ≈ 4 − 7 with the observed abundance and derived constraints for the evolution of the dark energy equation of state parameter which is complementary to the existing probes. The study employed three different, independent probes, namely the luminous end of the stellar mass function at z ≥ 6, the spatial density of luminous galaxies detected in the submillimeter range at z = 4 − 5, and the rareness of the extreme hyperluminous infrared galaxy SPT031158 at z ≈ 7. The analysis excluded a significant fraction of parameter spaces for the DDE models but interestingly does not completely exclude the possibility that dark energy may be dynamical (i.e, changing with time).

Deepest visible-light image of the Universe containing nearly 10000 galaxies. Source: Hubble

According to our current understanding of large scale structure formation, all cosmic structures are hypothesized to form from the gravitational collapse of density perturbations of enigmatic dark matter (DM) in a Universe characterized by an accelerated expansion. Such an acceleration indicates that the dominant component of the cosmic fluid must be in the form of mysterious dark energy (DE) with an equation-of-state (EoS) parameter close to -1. Although the nature of this entity is not known, one of the simplest models assumes DE to be connected with the vacuum energy, the so-called cosmological constant. This coupled with the added assumption that DM is non-dissipative, gives rise to the standard model in cosmology, also known as the LCDM model.

Although observations from the Cosmic Microwave Background (CMB) have provided strong confirmation of the LCDM model, however, there are some tensions that need to be properly sufficed including the famous Hubble tension. In this spirit, cosmologists have started to investigate the possibility of DE being dynamical in nature. Many studies have argued that if DE is indeed dynamical, it can solve many of the problems in modern cosmology which the LCDM model cannot.

The present study constrained the parameter spaces of DDE models and therefore rule out many of the proposed DDE models in the literature. However, the team reported that within the allowed parameter spaces, the Hubble tension could be resolved in some of the DDE models. The study also excluded the possibility of DE being quintessence in nature (EoS >-1).

Such studies are indeed important as they provide a consistency check for the standard LCDM model and concurrently checks the observational viability of the ever-increasing DDE models.

The study has been accepted for publication in The Astrophysical journal.

Article Information: N. Menci et al., "Constraints on Dynamical Dark Energy Models from the Abundance of Massive Galaxies at High Redshifts", arXiv: 2007.12453

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