Determining the Hubble constant using Giant extragalactic HII regions and HII galaxies

TL;DR

This study uses high-quality spectroscopic data of HII regions and galaxies to refine a distance indicator, enabling an independent measurement of the Hubble constant consistent with previous supernova-based estimates.

Contribution

It improves the L-sigma distance estimator for HII regions and galaxies, providing an independent and precise measurement of the Hubble constant.

Findings

H0 measured as 74.3 km/s/Mpc with ~4 km/s/Mpc total uncertainty

Results agree with recent supernova-based Hubble constant estimates

Refined the L(Hbeta)-sigma relation using local calibrators

Abstract

We report the first results of a long term program aiming to provide accurate independent estimates of the Hubble constant (H0) using the L-sigma distance estimator for Giant extragalactic HII regions (GEHR) and HII galaxies. We have used VLT and Subaru high dispersion spectroscopic observations of a local sample of HII galaxies, identified in the SDSS DR7 catalogue in order to re-define and improve the L(Hbeta)-sigma distance indicator and to determine the Hubble constant. To this end we utilized as local calibration or `anchor' of this correlation, GEHR in nearby galaxies which have accurate distance measurements determined via primary indicators. Using our best sample of 69 nearby HII galaxies and 23 GEHR in 9 galaxies we obtain H0=74.3 +- 3.1 (statistical) +- 2.9 (systematic) km /s Mpc, in excellent agreement with, and independently confirming, the most recent SNe Ia based results.