WHaD diagram: Classifying the ionizing source with one single emission line S. F. Sánchez, A. Z. Lugo-Aranda, J. Sánchez Almeida, J. K. Barrera-Ballesteros, O. Gonzalez-Martín, S. Salim and C. J. Agostino A&A, 682 (2024) A71 Published online: 02 February 2024 DOI: 10.1051/0004-6361/202347711