Navegando por Autor "Ilha, Gabriele da Silva"

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    Chemical abundances of LINER galaxies – nitrogen abundance estimations
    (Royal Astronomical Society) Oliveira Junior, Celso B.; Krabbe, Angela Cristina; Dors Junior, Oli Luiz; Zinchenko, Igor; Hernandez-Jimenez, Jose Andres; Cardaci, Mónica Viviana; Hagele, Guillermo F.; Ilha, Gabriele da Silva
    In this work, we investigated the nitrogen and oxygen abundances in a sample of galaxies with Low Ionization Nuclear Emission Regions (LINERs) in their nucleus. Optical spectroscopic data (3600 – 10 000 Å) of 40 LINERs from the Mapping Nearby Galaxies (MaNGAs) survey were considered. Only objects classified as retired galaxies, that is, whose main ionization sources are post-Asymptotic Giant Branch (pAGB) stars, were selected. The abundance estimates were obtained through detailed photoionization models built with the CLOUDY code to reproduce a set of observational emission line intensities ratios of the sample. Our results show that LINERs have oxygen and nitrogen abundances in the ranges of 8.0 􏰀 12 + log(O/H) 􏰀 9.0 (mean value 8.74 ± 0.27) and 7.6 􏰀 12 + log(N/H) 􏰀 8.5 (mean value 8.05 ± 0.25), respectively. About 70 per cent of the sample have oversolar O/H and N/H abundances. Our abundance estimates are in consonance with those for Seyfert 2 nuclei and H II regions with the highest metallicity, indicating that these distinct object classes show similar enrichment of the interstellar medium (ISM). The LINERs in our sample are located in the higher N/O region of the N/O versus O/H diagram, showing an unexpected negative correlation between these two parameters. These results suggest that these LINERs mainly exhibit a secondary nitrogen production and could be acting some other mechanisms that deviate them from the usual theoretical secondary nitrogen production curve and the H II regions observations. However, we did not find any evidence in our data able to support the literature suggested mechanisms. Alternatively, our results show that LINERs do not present any correlation between the N/O abundances and the stellar masses of the hosting galaxies.
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    Cosmic metallicity evolution of Active Galactic Nuclei: implications for optical diagnostic diagrams
    (Royal Astronomical Society) Dors Junior, Oli Luiz; Cardaci, Mónica Viviana; Hägele, Guilhermo F.; Ilha, Gabriele da Silva; Oliveira Junior, Celso Benedito de; Riffel, Rogemar A.; Riffel, Rogério; Krabbe, Angela Cristina
    We analyse the validity of optical diagnostic diagrams relying on emission-lines ratios and in the context of classifying Active Galactic Nuclei (AGNs) according to the cosmic metallicity evolution in the redshift range⁠. In this regard, we fit the results of chemical evolution models (CEMs) to the radial gradients of the N/O abundances ratio derived through direct estimates of electron temperatures (Te-method) in a sample of four local spiral galaxies. This approach allows us to select representative CEMs and extrapolate the radial gradients to the nuclear regions of the galaxies in our sample, inferring in this way the central N/O and O/H abundances. The nuclear abundance predictions for theoretical galaxies from the selected CEMs, at distinct evolutionary stages, are used as input parameters in AGN photoionization models built with the Cloudy code. We found that standard BPT diagnostic diagrams are able to classify AGNs with oxygen abundances at redshift. On the other hand, the He iiλ4685/Hβ versus [N ii]λ6584/Hα diagram produces a reliable AGN classification independent of the evolutionary stage of these objects.