Navegando por Autor "Santos, Pedro Camargo"

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    Metallicity of active galactic nuclei from ultraviolet and optical emission lines - II. Revisiting the C43 metallicity calibration and its implications
    (Oxford) Dors Junior, Oli Luiz; Oliveira, Celso Benedito de; Cardaci, Mónica Viviana; Hägele, Guillermo Federico; Armah, Mark; Riffel, Rogemar André; Vieira, Lucas Ramos; Almeida, Gleicy Caroline de; Morais, Istenio Nunes de; Santos, Pedro Camargo
    In this study, a new semi-empirical calibration is proposed between ultraviolet emission lines (CIII]λ1909, CIVλ1549, HeII]λ1640) of type 2 active galactic nuclei (AGNs) and their metallicity (Z). This calibration is derived by comparing a large sample of 106 objects (data taken from the literature) located over a wide range of redshifts (0 􏰁 z 􏰁 4.0) with predictions from photoionization models that adopt a recent C/O–O/H relation derived via estimates using the Te method, which is considered the most reliable method. We found that the new calibration produces Z values in agreement (within an uncertainty of ±0.1 dex) with those from other calibrations and from estimates via the Te-method. We find also that AGN metallicities are already high at early epochs, with no evidence for monotonic evolution across the redshift range 0 􏰁 z 􏰁 12. Notably, the highest metallicities in our sample, reaching up to 4 Z⊙, are found in objects at 2 􏰁 z 􏰁 3. This redshift range coincides with the peak of the cosmic star formation rate history, suggesting a strong connection between the major epoch of star formation, black hole growth, and rapid metal enrichment in the host galaxies of AGNs. Furthermore, our analysis reveals no significant correlation between AGN metallicity and radio properties (radio spectral index or radio luminosity) or host galaxy stellar mass. The lack of a clear mass–metallicity relation, consistent with findings for local AGNs, suggests that the chemical evolution of the nuclear gas is decoupled from the global properties of the host galaxy.
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    Metallicity of active galactic nuclei from ultraviolet and optical emission lines: I. Carbon abundance dependence
    (Royal Astronomical Society) Dors Junior, Oli Luiz; Oliveira Junior, Celso Benedito de; Cardaci, Mónica Viviana; Hagele, Guillermo Federico; Morais, Istenio Nunes de; Ji, Xihan; Riffel, Rogemar André; Riffel, Rogério; Mezcua, Mar; Almeida, Gleicy Caroline de; Santos, Pedro Camargo; Mellos, Maitê Silvana de Zorzi de
    Metallicity (Z) estimates based on ultraviolet (UV) emission lines from the narrow-line regions of active galactic nuclei (AGNs) have been found to differ from those derived from optical lines. However, the origin of this discrepancy (ZR) remains poorly understood. To investigate the source of ZR, we compiled from the literature the fluxes of narrow near- UV [1000 < λ(Å) < 2000] and optical [3000 < λ(Å) < 7000] emission-line measurements for a sample of 11 AGNs (nine at z < 0.4 and two at z ∼ 2.4). Metallicity values for our sample were derived using a semi-empirical calibration based on the C43 = log[(C IVλ1549 + C III]λ1909)/He IIλ1640] emission-line ratio and compared with those obtained via direct measurement of the electron temperature (Te-method) and via calibrations based on optical emission lines. The source of the discrepancy was investigated in terms of the ionization parameter (U), electron density (Ne), and carbon abundance (C/H). We found a weak correlation between ZR, U, and Ne. However, a moderate correlation was observed between ZR and direct estimates of C/H, suggesting that the previously assumed (C/O)–Z relations in photoionization models used to derive UV carbon-line calibrations may not be valid for AGNs. By combining a large set of abundance estimates for local star-forming regions with those of our AGN sample, we derived a new (C/O)–Z relation. Comparisons between the results of photoionization models that assume this new abundance relation and the UV observational data of our sample produce Z values derived from the C43 index that are consistent with those obtained using the Te-method.