We examine the relation between oxygen abundances in the narrow-line regions (NLRs) of active galactic nuclei (AGNs) estimated from the optical emission lines through the strong-line method (the theoretical calibration of Storchi-Bergmann et al. 1998), via the direct T e -method, and the central intersect abundances in the host galaxies determined from the radial abundance gradients. We found that the T e -method underestimates the oxygen abundances by up to ∼2 dex (with average value of ∼ 0.8 dex) compared to the abundances derived through the strong-line method. This confirms the existence of the so-called "temperature problem" in AGNs. We also found that the abundances in the centres of galaxies obtained from their spectra trough the strong-line method are close to or slightly lower than the central intersect abundances estimated from the radial abundance gradient both in AGNs and Star-forming galaxies. The oxygen abundance of the NLR is usually lower than the maximum attainable abundance in galaxies (∼2 times the solar value). This suggests that there is no extraordinary chemical enrichment of the NLRs of AGNs.

We present a semi-empirical calibration between the metallicity (Z) of Seyfert 2 Active Galactic Nuclei and the N 2=log([N ii]λ6584/Hα) emission-line intensity ratio. This calibration was derived through the [O iii]λ5007/[O ii]λ3727 versus N 2 diagram containing observational data and photoionization model results obtained with the Cloudy code. The observational sample consists of 463 confirmed Seyfert 2 nuclei (redshift z 0.4) taken from the Sloan Digital Sky Survey DR7 dataset. The obtained Z-N 2 relation is valid for the range 0.3 (Z/Z ⊙ ) 2.0 which corresponds to −0.7 (N 2) 0.6. The effects of varying the ionization parameter (U ), electron density and the slope of the spectral energy distribution on the Z estimations are of the order of the uncertainty produced by the error measurements of N 2. This result indicates the large reliability of our Z − N 2 calibration. A relation between U and the [O iii]/[O ii] line ratio, almost independent of other nebular parameter, was obtained.

We compare the oxygen abundance (O/H) of the Narrow Line Regions (NLRs) of Seyfert 2 AGNs obtained through strong-line methods and from direct measurements of the electron temperature (T e -method). The aim of this study is to explore the effects of the use of distinct methods on the range of metallicity and on the mass-metallicity relation of AGNs at low redshifts (z 0.4). We used the Sloan Digital Sky Survey (SDSS) and NASA/IPAC Extragalactic Database (NED) to selected optical (3000 < λ(Å) < 7000) emission line intensities of 463 confirmed Seyfert 2 AGNs. The oxygen abundance of the NLRs were estimated using the theoretical Storchi-Bergmann et al. calibrations, the semi-empirical N 2O2 calibration, the bayesian H ii-Chi-mistry code and the T e -method. We found that the oxygen abundance estimations via the strongline methods differ from each other up to ∼ 0.8 dex, with the largest discrepancies in the low metallicity regime (12 + log(O/H) 8.5). We confirmed that the T e -method underestimates the oxygen abundance in NLRs, producing unreal subsolar values. We did not find any correlation between the stellar mass of the host galaxies and the metallicity of their AGNs. This result is independent of the method used to estimate Z.

For 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 &lt; λ(Å) &lt; 7000] of 65 local Seyfert 2 nuclei (z &lt; 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 over-solar 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 Collaboration, i.e. $Y_{\rm p}^{Planck}=0.2471\pm 0.0003$.

GMOS-IFU observational data were used to study the detailed two dimensional gas kinematics and morphological structures within the ∼ 500 × 421 pc 2 of the active Seyfert 2 galaxy NGC 4501. We provide empirical evidences of possible outflowing material from the central zones of NGC 4501 to the observer. In addition, we performed a spectral synthesis and diagnostic diagram analysis to determine respectively the dominant stellar population in the inner disc of this galaxy and to unveil the actual nature of the central engine of NGC 4501. The principal finding of this work is that the central regions of NGC 4501 are dominated by non circular motions connected to probable outflows of matter from the nuclear regions of this galaxy. A predominant old stellar population inhabits the internal zones of NGC 4501 excluding the possibility of ongoing starburst activity in the central parsecs of this galaxy. The latter result is confirmed by the diagnostic diagram analysis that establishes a preponderant active galactic nucleus character for NGC 4501. These outcomes together provide a general description of the gas motion and the corresponding nuclear activity in the internal disc of NGC 4501 in an attempt to elucidate the possible relation among the central activity and the induced kinematic properties of this nearby galaxy.

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Interactions between galaxies are very common. There are special types of interactions that produce systems called polar ring galaxies (PRGs), composed of a lenticular, elliptical or spiral host galaxy, surrounded by a ring of stars and gas, orbiting in an approximately polar plane.In this paper, we study AM 2020-504, a PRG with an elliptical host galaxy, and a narrow and well-defined ring, probably formed by accretion of material from a donor galaxy, collected by the host galaxy. Our observational study is based on BVRI broad-band imagery as well as long-slit spectroscopy in the wavelength range 4100-8600 Å, performed at the 1.6-m telescope at the Observatório do Pico dos Dias, Brazil. We have estimated a redshift of z = 0.01683, corresponding to a heliocentric radial velocity of 5045 ± 23 km s −1 . The (B − R) colour map shows that the ring is bluer than the host galaxy, which indicates that the ring is a younger structure. Standard diagnostic diagrams have been used to classify the main ionizing source of selected emission-line regions (nucleus, host galaxy and ring). We find that the ring regions are mainly ionized by massive stars, while the nucleus presents the characteristics of an active galactic nucleus. Using two empirical methods, we have found oxygen abundances for the H II regions located in the ring in the range 12+log(O/H) = 8.3-8.8 dex. We have also found the presence of an oxygen gradient across the ring, and it appears that AM 2020-504 follows the metallicity-luminosity relation of spiral galaxies. These results support the accretion scenario for this object and they rule out cold accretion as the source for the H I gas in the polar ring.

ABSTRACT This contribution aims to study the nature (kinematic, nuclear activity, and stellar population) of a sample of 10 galaxies in the poor cluster Abell S0805. As no detailed optical spectroscopy for some members has been published yet, the selected sample makes this study ideal for investigating the properties of the following objects: ESO 104- G(002, 006, 007, 008, 009, 010, 013), Fairall 0187, and PGC (062384, 062391). Our main results were obtained after subtraction of the underlying stellar population with the spectral synthesis code starlight. The residual spectra reveal seven galaxies with only absorption lines [ESO 104- G(002, 007, 008, 009), Fairall 0187 and PGC (062384, 062391)], and three galaxies with emission lines [ESO 104- G(006, 010, 013)]. According to the boundaries in the diagnostic diagrams, the intensities of H α and the low-ionization lines ([N ii] λ6584 Å and [S ii] λλ6716,6731 Å) suggest the following results: (i) the brightest cluster galaxy (ESO 104- G006, an elliptical cD galaxy) shows low-ionization nuclear emission-line region (LINER)-like excitation, quite common in ‘cool core clusters’; (ii) the ESO 104- G010 (‘X-Galaxy’ or ‘Crystal Frog’) shows an excess of the nitrogen emission-line [N ii] λ6584 Å not yet reported. We also suggest this object as a LINER; (iii) the spiral ESO 104- G013 is a star-forming galaxy with typical emission lines. No obvious signs of interaction were observed in this study. The heliocentric velocities agree within 1σ with the most recent values. The stellar population, rotation curves, and velocity dispersions are also discussed for the first time for some objects.