GALÁXIAS HII COMO INDICADORAS DE DISTÂNCIAS - APRIMORAMENTO DA RELAÇÃO L − σ

Abstract

HII galaxies (HIIG) are a subgroup of extremely bright, starburst compact dwarf irregular galaxies that carry an empirical correlation between velocity scattering (σ), observed from the width of the emission lines and luminosity (LHα and LHβ) of the Balmer series lines. This relation makes the HIIG an alternative to the well-known standard candles (type Ia supernova) as a standard relations because it is possible to estimate distances and cosmological parameters from it. Improving the relation has been one of the main goals in the studies of this class of galaxies since its discovery and also the main motivation for this work. We investigated the dependence of the L − σ relation for a second parameter. We estimate to calibrate it to a bi-parametric relation with the inclusion of a parameter that explains the origin of the enlargement observed in the emission lines, or that is related to the physical properties of the evolution of these galaxies. The two approaches were studied individually and separated in "Acts". In Act I, we worked with the hypothesis that the broadening of the lines originates in virialized movements, similar to that observed in gravitationally bound galaxies. The second parameter was the galactic radius. For this, we rely on narrowband images of Hβ for 39 HIIG obtained from the ESO NTT 3.58m telescope, where it was possible to obtain good size measurements for two petrosian rays: R_petro, which considers the flux petrosian of the galaxy, and R_50, the effective radius that incorporates 50% of the total flux. From this analysis we were able to study in detail the characteristics of the Petrosian ray and what is actually measured in the SDSS images. Our images have better spatial and S/N resolution than those of the SDSS, thus delivering more details of the structures of galaxies and allowing us to perform better radius measurements. However, from this study we also demonstrate that the size parameter is not a good option to calibrate the empirical relation. In act II we investigated the spectroscopic parameters associated with the evolution of HII galaxies, the chemical abundance O/H and the equivalent width WHβ, the latter being an indicator of the age of the star formation regions. In this stage of the work, we have a robust sample of 207 HII galaxies, resulting from the combination of 2 works by members of the group (Bordalo and Telles (2011); Chavez et al. (2014)) and a completely new sample of HIIG. Our results indicate that possibly the L − σ relation has an effect due to the burst of current stellar evolution. Currently, the L − σ relation has a lower performance than the SNIa in determining distances and, consequently, cosmological parameters. However, the perspective is that improvements in the relation through the insertion of a second parameter, as explored in this work, can help the existing calibration methods of the HIIG and, in the future, allow us to achieve more accurate distance indicators. The result will allow a comparison between these independent indicators and the understanding of the systematic effects of the two methods.