@ARTICLE{2026A&A...710L..28P,
       author = {{P{\'e}rez-D{\'\i}az}, Borja and {V{\'\i}lchez}, Jos{\'e} M. and {Castellano}, Marco and {Amor{\'\i}n}, Ricardo and {Bevacqua}, Davide and {Fontana}, Adriano and {Gandolfi}, Giovanni and {Gim{\'e}nez-Alc{\'a}zar}, Antonio and {Pentericci}, Laura and {P{\'e}rez-Montero}, Enrique and {Santini}, Paola and {Tripodi}, Roberta},
        title = "{Beyond the [O III]{\ensuremath{\lambda}}4363 auroral line: [Ne III]{\ensuremath{\lambda}}3868 as a direct tracer of the electron temperature}",
      journal = {\aap},
     keywords = {ISM: abundances, ISM: general, galaxies: abundances, galaxies: active, galaxies: ISM},
         year = 2026,
        month = jun,
       volume = {710},
          eid = {L28},
        pages = {L28},
     abstract = "{Context. 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. Aims. To
        overcome this limitation, we present a novel approach to
        estimating electron temperatures in conditions where the [O
        III]{\ensuremath{\lambda}}4363 auroral line is barely detectable
        (T$_{e}$ < 11 000 K). This approach relies on the detection of
        [Ne III]{\ensuremath{\lambda}}3868 and [O
        III]{\ensuremath{\lambda}}4959,5007, which are among the
        brightest rest-frame optical emission lines. Methods. By means
        of detailed photoionization models, we derived a tight relation
        between the O3Ne3 {\ensuremath{\equiv}}[O
        III]{\ensuremath{\lambda}}4959,5007/[Ne
        III]{\ensuremath{\lambda}}3868 ratio and the electron
        temperature weighted in the O$^{++}$ dominated region. We tested
        the validity of this relation in a large sample of galaxies that
        cover a wide range of redshifts z {\ensuremath{\sim}} 0─9 and
        extragalactic HII regions. Results. 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 [O
        III]{\ensuremath{\lambda}}4363. The proposed relation can be
        used to estimate the electron temperature in the cool
        (equivalently, high-metal) regime [6000, 13 500 K] where the
        emissivity of [O III]{\ensuremath{\lambda}}4363 drops
        drastically.}",
          doi = {10.1051/0004-6361/202660294},
       adsurl = {https://ui.adsabs.harvard.edu/abs/2026A&A...710L..28P},
      adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}