The Dark Energy Equation of State using Alternative High-z Cosmic Tracers

TL;DR

This paper introduces a novel approach using high-redshift HII galaxies and X-ray AGN clustering to constrain dark energy properties, offering an alternative to supernova-based methods and reducing systematic uncertainties.

Contribution

It proposes combining HII galaxy Hubble relation measurements with AGN clustering data to improve constraints on dark energy and matter content, breaking parameter degeneracies.

Findings

Joint analysis yields Omega_m=0.27+-0.02 and w≈-0.96 to -0.97.

Method reduces systematic errors compared to traditional techniques.

Results are consistent with WMAP5 and BAO measurements.

Abstract

We propose to use alternative cosmic tracers to measure the dark energy equation of state and the matter content of the Universe [w(z) & Omega_m]. Our proposed method consists of two components: (a) tracing the Hubble relation using HII galaxies which can be detected up to very large redshifts, z~4, as an alternative to supernovae type Ia, and (b) measuring the clustering pattern of X-ray selected AGN at a median redshift of z~1. Each component of the method can in itself provide interesting constraints on the cosmological parameters, especially under our anticipation that we will reduce the corresponding random and systematic errors significantly. However, by joining their likelihood functions we will be able to put stringent cosmological constraints and break the known degeneracies between the dark energy equation of state (whether it is constant or variable) and the matter content of the universe and provide a powerful and alternative route to measure the contribution to the global dynamics and the equation of state of dark energy. A preliminary joint analysis of X-ray selected AGN (based on the largest to-date XMM survey; the 2XMM) and the currently largest SNIa sample (Hicken et al.), using as priors a flat universe and the WMAP5 normalization of the power-spectrum, provides: Omega_m=0.27+-0.02 and w=-0.96+-0.07. Equivalent and consistent results are provided by the joint analysis of X-ray selected AGN clustering and the latest Baryonic Acoustic Oscillation measures, providing: Omega_m=0.27+-0.02 and w=-0.97+-0.04.