Neon and argon optical emission lines in ionized gaseous nebulae: implications and applications

In this work, we present a study of the strong optical collisional emission lines of Ne and Ar in an heterogeneous sample of ionized gaseous nebulae for which it is possible to derive directly the electron temperature and hence the chemical abundances of Ne and Ar. We calculate using a grid of photoionization models new ionization correction factors for these two elements and we study the behaviour of Ne/O and Ar/O abundance ratios with metallicity. We find a constant value for Ne/O, while there seems to be some evidence for the existence of negative radial gradients of Ar/O over the discs of some nearby spirals. We study the relation between the intensities of the emission lines of [Ne  iii ] at 3869 Å and [O  iii ] at 4959 and 5007 Å. This relation can be used in empirical calibrations and diagnostic ratios extending their applicability to bluer wavelengths and therefore to samples of objects at higher redshifts. Finally, we propose a new diagnostic using [O  ii ], [Ne  iii ] and Hδ emission lines to derive metallicities for galaxies at high z .