Constraining the Parameter Space of the Dark Energy Equation of State Using Alternative Cosmic Tracers

TL;DR

This study uses HII galaxies as alternative cosmic tracers to constrain dark energy parameters, providing an independent check on cosmological models and measuring the Hubble constant with results consistent with supernova-based estimates.

Contribution

It introduces a method using HII galaxies' $L(H\beta)-\sigma$ relation to constrain dark energy parameters and measure $H_0$, offering an alternative to supernova-based cosmology.

Findings

The $L(H\beta)-\sigma$ relation is strong and stable across samples.

Measured $H_0$ as 74.3 km s$^{-1}$ Mpc$^{-1}$, consistent with supernova results.

Provided constraints on $H_0$, $\Omega_m$, and dark energy equation of state parameters.

Abstract

We propose to use HII galaxies (HIIG) to trace the redshift-distance relation, by means of their $L(\mathrm{H}\beta) - \sigma$ correlation, in an attempt to constrain the dark energy equation of state parameter solution space, as an alternative to the cosmological use of type Ia supernovae. For a sample of 128 local compact HIIG with high equivalent widths of their Balmer emission lines we obtained ionised gas velocity dispersion from high S/N, high-dispersion spectroscopy (Subaru-HDS and ESO VLT-UVES) and integrated H$\beta$ fluxes from low dispersion wide aperture spectrophotometry. We find that the $L(\mathrm{H}\beta) - \sigma$ relation is strong and stable against restrictions in the sample. The size of the starforming region is an important second parameter, while adding the emission line equivalent width or the continuum colour and metallicity, produces the solution with the smallest rms scatter. We have used the $L(\mathrm{H}\beta) - \sigma$ relation from a local sample of HIIG and a local calibration or `anchor', given by giant HII regions in nearby galaxies which have accurate distance measurements determined via primary indicators, to obtain a value of $H_0$. Using our best sample of 69 HIIG and 23 Giant HII regions in 9 galaxies we obtain $H_{0}=74.3 \pm 3.1$ (statistical)$\pm$ 2.9 (systematic) km s$^{-1}$ Mpc$^{-1}$, in excellent agreement with, and independently confirming, the most recent SNa Ia based results. Using a local sample (107 sources) and a sample of 21 high redshift HIIG, 6 of them with medium-dispersion spectroscopy (ESO VLT-XShooter) and 17 taken from the literature, we have obtained constraints on the planes $H_0 - \Omega_m$, $\Omega_m - w_0$ and $w_0 - w_1$ (CPL model).