Constraining the Dark Energy Equation of State with HII Galaxies

TL;DR

This study utilizes high-redshift HII galaxies and their $L - \sigma$ relation, combined with other cosmological probes, to constrain the dark energy equation of state, showing promising results and potential for significant future improvements.

Contribution

It demonstrates the viability of using HII galaxies as a cosmological probe for dark energy, with simulations indicating substantial improvements with larger samples.

Findings

Current HII galaxy data provides constraints consistent with SNIa.

Joint analysis improves dark energy constraints by 13%.

Simulations show potential for major improvements with 500 high-z HII galaxies.

Abstract

We use the HII galaxies $L - \sigma$ relation and the resulting Hubble expansion cosmological probe of a sample of just 25 high-$z$ (up to $z \sim 2.33$) HII galaxies, in a joint likelihood analysis with other well tested cosmological probes (CMB, BAOs) in an attempt to constrain the dark energy equation of state (EoS). The constraints, although still weak, are in excellent agreement with those of a similar joint analysis using the well established SNIa Hubble expansion probe. Interestingly, even with the current small number of available high redshift HII galaxies, the HII/BAO/CMB joint analysis gives a 13% improvement of the quintessence dark energy cosmological constraints compared to the BAO/CMB joint analysis. We have further performed extensive Monte Carlo simulations, with a realistic redshift sampling, to explore the extent to which the use of the $L - \sigma$ relation, observed in HII galaxies, can constrain effectively the parameter space of the dark energy EoS. The simulations predict substantial improvement in the constraints when increasing the sample of high-$z$ HII galaxies to 500, a goal that can be achieved in reasonable observing times with existing large telescopes and state-of-the-art instrumentation.