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Keywords:

  • ii regions;
  • cosmological parameters;
  • distance scale

ABSTRACT

We report the first results of a long-term programme aiming to provide accurate independent estimates of the Hubble constant (H0) using the L(Hβ)–σ distance estimator for giant extragalactic H ii regions (GEHR) and H ii galaxies.

We have used Very Large Telescope and Subaru high-dispersion spectroscopic observations of a local sample of H ii galaxies, identified in the Sloan Digital Sky Survey Data Release 7 (SDSS DR7) catalogue in order to redefine and improve the L(Hβ)–σ 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 H ii galaxies and 23 GEHR in nine galaxies, we obtain H0= 74.3 ± 3.1 (statistical) ± 2.9 (systematic) km s−1 Mpc−1, in excellent agreement with, and independently confirming, the most recent Type Ia supernovae based results.