Melnick J., Telles E., Bordalo V., Chávez R., Fernández-Arenas D., Terlevich E., Terlevich R., Bresolin, F. Plionis M., Basilakos S.

Astronomy & Astrophysics, Volume 599, id.A76, 13 pp.

Publication year: 2017

**Summary **

The correlation between emission-line luminosity (*L*) and profile-width (*σ*) for HII galaxies provides a powerful method to measure the distances to galaxies over a wide range of redshifts. In this paper, we use SDSS spectrophotometry to explore the systematics of the correlation using the [OIII]5007 lines instead of H*α* or H*β* to measure luminosities and line widths. We also examine possible systematic effects involved in measuring the profile-widths and the luminosities through different apertures. We find that the green *L*−*σ* relation, defined using [OIII]5007 luminosities, is significantly more sensitive than H*β* to the effects of age and the physical conditions of the nebulae, which more than offsets the advantage of the higher strength of the [OIII]5007 lines. We then explore the possibility of mixing [OIII]5007 profile-widths with SDSS H*β* luminosities using the Hubble constant *H*_{0} to quantify the possible systematic effects. We find the mixed *L*(H*β*) − *σ*_{[OIII]} relation to be at least as powerful as the canonical *L*−*σ* relation as a distance estimator, and we show that evolutionary corrections do not change the slope and the scatter of the correlation and, therefore, do not bias the *L*−*σ* distance indicator at high redshifts. Locally, however, the luminosities of the giant HII regions that provide the zero-point calibrators are sensitive to evolutionary corrections and may bias the Hubble constant if their mean ages, as measured by the equivalent widths of H*β*, are significantly different from the mean age of the HII galaxies. Using a small sample of 16 ad-hoc zero point calibrators we obtain a value of *H*_{0} = 66.4^{+ 5.0}_{-4.5}km s^{-1} Mpc^{-1} for the Hubble constant, which is fully consistent with the best modern determinations, and which is not biased by evolutionary corrections.