Beyond the [OIII]l4363 auroral line: [NeIII]l3868 as a direct tracer of the electron temperature

Auroral lines enable accurate measurements of chemical abundances in ionized gaseous nebulae because they are sensitive to the electron temperature. However, metal-enriched systems remain a challenge because even deep observations cannot retrieve auroral lines: they are intrinsically faint. To overcome this limitation, we present a novel approach to estimating electron temperatures in conditions where the auroral line is barely detectable (T_ 4363 e < 11,000 K). This approach relies on the detection of , which are among the brightest rest-frame optical emission lines. and 4959,5007 By means of detailed photoionization models, we derived a tight relation between the O3Ne3≡ / $ dominated region. We tested the validity of this relation in a large sample of galaxies that cover a wide range of redshifts z$∼0-9 and extragalactic HII regions. 4959,5007 ratio and the electron temperature weighted in the O ++ Our results show that the O3Ne3 ratio, in combination with the O3O2 ratio (tracer of ionization), yields electron temperature estimates that are consistent within the uncertainties with those based on . The proposed relation can be used to estimate the electron temperature in the cool (equivalently, high-metal) regime 4363 6,000, 13,500 K where the emissivity of drops drastically. 4363