Dors Junior, Oli LuizValerdi, MabelLemes, Priscila FreitasKrabbe, Angela CristinaRiffel, Rogemar AndréAmôres, Eduardo BrescansinRiffel, RogérioArmah, MarkMonteiro, Adriano FranciscoOliveira Junior, Celso Benedito de2025-03-142025-03-14https://repositorio.univap.br/handle/123456789/697For the first time, the helium abundance relative to hydrogen (He/H), which relied on direct measurements of the electron temperature, has been derived in the narrow line regions (NLRs) from a local sample of Seyfert 2 nuclei. In view of this, optical emission line intensities [3000 < λ(Å) < 7000] of 65 local Seyfert 2 nuclei (z < 0.2), taken from Sloan Digital Sky Survey Data Release 15 and additional compilation from the literature, were considered. We used photoionization model grid to derive an Ionization Correction Factor (ICF) for the neutral helium. The application of this ICF indicates that the NLRs of Seyfert 2 present a neutral helium fraction of ∼50 per cent in relation to the total helium abundance. We find that Seyfert 2 nuclei present helium abundance ranging from 0.60 to 2.50 times the solar value, while ∼85 per cent of the sample present oversolar abundance values. The derived (He/H)–(O/H) abundance relation from the Seyfert 2 is stepper than that of star-forming regions (SFs) and this difference could be due to excess of helium injected into the interstellar medium by the winds of Wolf–Rayet stars. From a regression to zero metallicity, by using Seyfert 2 estimates combined with SFs estimates, we obtained a primordial helium mass fraction Yp = 0.2441 ± 0.0037, a value in good agreement with the one inferred from the temperature fluctuations of the cosmic microwave background by the Planck CollaborationPDFen-USArtigos de PeriódicosMonthly Notices of the Royal Astronomical Society10.1093/mnras/stac1722Galaxies: abundancesGalaxies: activeGalaxies: evolutionGalaxies: formationGalaxies: ISMGalaxies: nucleiDORS JUNIOR, Oli Luiz et al. Chemical abundances in Seyfert galaxies – IX. Helium abundance estimates. Monthly Notices of the Royal Astronomical Society, v. 514, n. 4, p. 5506-5527, 2022. Disponível em:Universidade do Vale do ParaíbaInstituto Nacional de Astrofísica, Óptica y Electrónica (INAOE)Universidade Federal de Santa MariaUniversidade Estadual de Feira de SantanaUniversidade Federal do Rio Grande do SulInstituto Federal do Maranhão