Extreme emission line galaxies (EELGs) are key tracers of intense star formation and potential analogues of the sources that reionized the early Universe. Their low-redshift counterparts offer a unique opportunity to study the physical conditions that enable high ionizing-photon escape fractions. We present a robust method to photometrically identify EELGs in the J-PAS survey, which provides 56 optical bands over 8500 deg^2. Using data from a fully observed 30 deg^2 region, we combine narrow-band equivalent widths with machine-learning techniques to select galaxies with emission lines above 300 {\AA}. The method achieves 95% purity and 96% completeness for iSDSS<22.5 mag. We identify 917 EELGs up to z=0.8; spectroscopic cross-matching with DESI/DR1 confirms the reliability of our redshifts and emission-line measurements. The selected galaxies show strong correlations between ξion and EW([OIII]), consistent with previous low- and high-z studies. Most sources exceed the ionizing efficiency threshold required for reionization, reinforcing their role as local analogues of early-Universe galaxies.
@article{arxiv.2512.08484,
title = {J-PAS: First Identification, Physical Properties and Ionization Efficiency of Extreme Emission Line Galaxies},
author = {A. Giménez-Alcázar and R. Amorín and J. M. Vílchez and A. Hernán-Caballero and M. González-Otero and A. Arroyo-Polonio and J. Iglesias-Páramo and A. Lumbreras-Calle and J. A. Fernández-Ontiveros and L. Bonatto and R. M. González Delgado and C. Kehrig and A. Torralba and P. T. Rahna and Y. Jiménez-Teja and I. Márquez and I. Breda and A. Álvarez-Candal and R. Abramo and J. Alcaniz and N. Benitez and S. Bonoli and S. Carneiro and J. Cenarro and D. Cristóbal-Hornillos and R. Dupke and A. Ederoclite and C. Hernández-Monteagudo and A. Marín-Franch and C. Mendes de Oliveira and M. Moles and L. Sodré and K. Taylor and J. Varela and H. Vázquez Ramió},
journal= {arXiv preprint arXiv:2512.08484},
year = {2026}
}