On the road to precision cosmology with high redshift HII galaxies

TL;DR

This study explores high redshift HII galaxies to improve constraints on dark energy's equation of state using the $L(H\beta)-\sigma$ relation, demonstrating the potential of future high-quality data for precision cosmology.

Contribution

It presents the first high-resolution spectroscopic analysis of high-z HII galaxies for cosmological constraints and highlights the need for larger, high-quality samples.

Findings

Constraints on $\Omega_m - w_0$ plane are obtained.

High-z HII galaxies can provide competitive cosmological constraints.

Future larger samples with better data can significantly improve results.

Abstract

We report the first results of a programme aimed at studying the properties of high redshift galaxies with on-going massive and dominant episodes of star formation (HII galaxies). We use the $L(\mathrm{H}\beta) - \sigma$ distance estimator based on the correlation between the ionized gas velocity dispersions and Balmer emission line luminosities of HII galaxies and Giant HII regions to trace the expansion of the Universe up to $z \sim 2.33$. This approach provides an independent constraint on the equation of state of dark energy and its possible evolution with look-back time. Here we present high-dispersion (8,000 to 10,000 resolution) spectroscopy of HII galaxies at redshifts between 0.6 and 2.33, obtained at the VLT using XShooter. Using six of these HII galaxies we obtain broad constraints on the plane $\Omega_m - w_0$. The addition of 19 high-z HII galaxies from the literature improves the constraints and highlights the need for high quality emission line profiles, fluxes and reddening corrections. The 25 high-z HII galaxies plus our local compilation of 107 HII galaxies up to $z=0.16$ were used to impose further constraints. Our results are consistent with recent studies, although weaker due to the as yet small sample and low quality of the literature data of high-z HII galaxies. We show that much better and competitive constraints can be obtained using a larger sample of high redshift HII galaxies with high quality data that can be easily obtained with present facilities like KMOS at the VLT.