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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 |$0 \le z \le 11.2$|⁠. 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 (T e-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 |$\rm 12+\log (O/H) \gtrsim 8.0$| [ |$(Z/Z_{\odot }) \gtrsim 0.2$| ] at redshift |$z \lesssim 4$|⁠. On the other hand, the He  ii λ4685/Hβ versus [N  ii ]λ6584/Hα diagram produces a reliable AGN classification independent of the evolutionary stage of these objects. [ABSTRACT FROM AUTHOR]

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, via the direct Te-method, and the central intersect abundances in the host galaxies determined from the radial abundance gradients. We found that the Te-method underestimates the oxygen abundances by up to ~2 dex (with averaged 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. [ABSTRACT FROM AUTHOR]

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 |$\rm 8.0 \: \lesssim \: 12+\log (O/H) \: \lesssim \: 9.0$| (mean value 8.74 ± 0.27) and |$\rm 7.6 \: \lesssim \: 12+\log (N/H) \: \lesssim \: 8.5$| (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. [ABSTRACT FROM AUTHOR]

We investigate the discrepancy between oxygen abundance estimations for narrow-line regions of active galactic nuclei (AGNs) type Seyfert 2 derived using direct estimations of the electron temperature (T e-method) and those derived using photoionization models. In view of this, observational emission-line ratios in the optical range (⁠|$3000 \: \lt \: \lambda (\mathring{\rm A}) \: \lt 7000$|⁠) of Seyfert 2 nuclei compiled from the literature were reproduced by detailed photoionization models built with the cloudy code. We find that the derived discrepancies are mainly due to the inappropriate use of the relations between temperatures of the low (t 2) and high (t 3) ionization gas zones derived for H  ii regions in AGN chemical abundance studies. Using a photoionization model grid, we derived a new expression for t 2 as a function of t 3 valid for Seyfert 2 nuclei. The use of this new expression in the AGN estimation of the O/H abundances based on T e-method produces O/H abundances slightly lower (about 0.2 dex) than those derived from detailed photoionization models. We also find that the new formalism for the T e-method reduces by about 0.4 dex the O/H discrepancies between the abundances obtained from strong emission-line calibrations and those derived from direct estimations. [ABSTRACT FROM AUTHOR]

We present a semi-empirical calibration between the metallicity (Z) of Seyfert 2 active galactic nuclei and the N2 = log([N  ii ]λ6584/H α) emission-line intensity ratio. This calibration was derived through the [O  iii ]λ5007/[O  ii ]λ3727 versus N2 diagram containing observational data and photoionization model results obtained with the cloudy code. The observational sample consists of 463 confirmed Seyfert 2 nuclei (redshift |$z \: \lesssim 0.4$|⁠) taken from the Sloan Digital Sky Survey DR7 data set. The obtained Z –N2 relation is valid for the range |$0.3 \: \lesssim \: (Z/{\rm Z}_{\odot }) \: \lesssim \: 2.0$| that corresponds to |$-0.7 \: \lesssim \: ({\rm N}2) \: \lesssim \: 0.6$|⁠. 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 N2. This result indicates the large reliability of our Z –N2 calibration. A relation between U and the [O  iii ]/[O  ii ] line ratio, almost independent of other nebular parameter, was obtained. [ABSTRACT FROM AUTHOR]

For the first time, the sulphur abundance relative to hydrogen (S/H) in the narrow-line regions of a sample of Seyfert 2 nuclei (Sy 2s) has been derived via direct estimation of the electron temperature. Narrow emission-line intensities from the Sloan Digital Sky Survey (SDSS) Data Release 17 (DR17) [in the wavelength range 3000 < λ(Å) < 9100] and from the literature for a sample of 45 nearby (z  < 0.08) Sy 2s were considered. Our direct estimates indicate that Sy 2s have similar temperatures in the gas region where most of the |$\rm S\rm ^{+}$| ions are located in comparison with that of star-forming regions (SFs). However, Sy 2s present higher temperature values (⁠|${\sim} 10\, 000$|  K) in the region where most of the |$\rm S\rm ^{2+}$| ions are located relative to that of SFs. We derive the total sulphur abundance in the range of |$6.2 \: \lesssim 12+\log (\rm S/H) \: \lesssim \: 7.5$|⁠ , corresponding to 0.1–1.8 times the solar value. These sulphur abundance values are lower by ∼0.4 dex than those derived in SFs with similar metallicity, indicating a distinct chemical enrichment of the interstellar medium (ISM) for these object classes. The sulphur abundance relative to oxygen (S/O) values for our Sy 2 sample present an abrupt (∼0.5 dex) decrease with increasing oxygen abundance relative to hydrogen (O/H) for the high-metallicity regime [ |$\rm 12+\log (O/H) \: \gtrsim 8.7)$| ], what is not seen for the SFs. However, when our Sy 2 estimates are combined with those from a large sample of SFs, we did not find any dependence between S/O and O/H. [ABSTRACT FROM AUTHOR]

We obtained new quantitative determinations of the nitrogen abundance and a consistent relation between the nitrogen and oxygen abundances for a sample of Seyfert 2 galaxies located at redshift z < 0.1.We carried out this analysis using the CLOUDY code to build detailed photoionization models. We were able to reproduce observed optical narrow emission line intensities for 44 sources compiled from the literature. Our results show that Seyfert 2 nuclei have nitrogen abundances ranging from ~0.3 to ~7.5 times the solar value. We derived the relation log(N/H) = 1.05(±0.09) × [log(O/H)] - 0.35(±0.33). Results for N/O versus O/H abundance ratios derived for Seyfert 2 galaxies are in consonance with those recently derived for a sample of extragalactic disc HII regions with high metallicity. [ABSTRACT FROM AUTHOR]

We derive a new relation between the metallicity of Seyfert 2 active galactic nuclei (AGNs) and the intensity of the narrow emission-lines ratio N2O2 = log([N П] λ6584/[O П] λ3727). The calibration of this relation was performed by determining the metallicity (Z) of a sample of 58 AGNs through a diagram containing the observational data and the results of a grid of photoionization models obtained with the CLOUDY code. We find the new Z/Z☉-N2O2 relation using the obtained metallicity values and the corresponding observational emissionline intensities for each object of the sample. Estimations derived through the use of this new calibration indicate that the narrow-line regions of Seyfert 2 galaxies exhibit a large range of metallicities (0.3 ≲ Z/Z☉ ≲ 2.0), with a median value Z ≈ Z☉. Regarding the possible existence of correlations between the luminosity L(Hβ), the electron density and the colour excess E(B-V) with themetallicity in this kind of objects, we do not find correlations between them. [ABSTRACT FROM AUTHOR]

The ionizing source of low-ionization nuclear emission-line regions (LINERs) is uncertain. Because of this, an empirical relation to determine the chemical abundances of these objects has not been proposed. In this work, for the first time, we derived two semi-empirical calibrations based on photoionization models to estimate the oxygen abundance of LINERS as a function of the N 2 and O 3 N 2 emission-line intensity ratios. These relations were calibrated using oxygen abundance estimations obtained by comparing the observational emission-line ratios of 43 LINER galaxies (taken from the MaNGA survey) and grids of photoionization models built with the cloudy code assuming post-asymptotic giant branch stars with different temperatures. We found that the oxygen abundance of LINERs in our sample is in the |$\rm 8.48 \: \lesssim \: 12+log(O/H) \: \lesssim 8.84$| range, with a mean value of |$\rm 12+\log (O/H)=8.65$|⁠. We recommend the use of the N 2 index to estimate the oxygen abundances of LINERs, since the calibration with this index presented a much smaller dispersion than the O 3 N 2 index. In addition, the estimated metallicities are in good agreement with those derived by extrapolating the disc oxygen abundance gradients to the centre of the galaxies showing that the assumptions of the models are suitable for LINERs. We also obtained a calibration between the logarithm of the ionization parameter and the [O  iii ]/[O  ii ] emission-line ratio. [ABSTRACT FROM AUTHOR]

Chemical abundance determinations in Low-Ionization Nuclear Emission-line Regions (LINERs) are especially complex and uncertain because the nature of the ionizing source of this kind of object is unknown. In this work, we study the oxygen abundance in relation to the hydrogen abundance (O/H) of the gas phase of the UGC 4805 LINER nucleus. Optical spectroscopic data from the Mapping Nearby Galaxies survey was employed to derive the O/H abundance of the UGC 4805 nucleus based on the extrapolation of the disc abundance gradient, on calibrations between O/H abundance and strong emission-lines for active galactic nuclei (AGNs) as well as on photoionization models built with the Cloudy code, assuming gas accretion into a black hole (AGN) and post-asymptotic giant branch (p-AGB) stars with different effective temperatures. We found that abundance gradient extrapolations, AGN calibrations, AGN, and p-AGB photoionization models produce similar O/H values for the UGC 4805 nucleus and similar ionization parameter values. The study demonstrated that the methods used to estimate the O/H abundance using nuclear emission-line ratios produce reliable results, which are in agreement with the O/H values obtained from the independent method of galactic metallicity gradient extrapolation. Finally, the results from the WHAN diagram combined with the fact that the high excitation level of the gas has to be maintained at kpc scales, we suggest that the main ionizing source of the UGC 4805 nucleus probably has a stellar origin rather than an AGN. [ABSTRACT FROM AUTHOR]

We build detailed composite models of photoionization and shock ionization based on the suma code to reproduce emission lines emitted from the Narrow Line Regions (NLR) of Seyfert 2 nuclei. The aim of this work is to investigate diagram active galactic nucleus (AGN) positions according to shock parameters, shock effects on the gas temperature and ionization structures and derive a semi-empirical abundance calibration based on emission-line ratios little sensitive to the shock presence. The models were used to reproduce optical (3000 < λ(Å) < 7000) emission line intensities of 244 local (⁠|$z \: \lesssim \: 0.4$|⁠) Seyfert 2s, whose observational data were selected from Sloan Digital Sky Survey DR7. Our models suggest that shocks in Seyfert 2 nuclei have velocities in the range of 50–300  |$\rm km \: s^{-1}$| and imply a narrower metallicity range (⁠|$0.6 \: \lesssim \: (Z/Z_{\odot }) \: \lesssim \: 1.6$|⁠) than those derived using pure photoionization models. Our results indicate that shock velocity in AGNs cannot be estimated using standard optical line ratio diagrams, based on integrated spectra. Our models predict a different temperature structure and |$\rm O^{+}$| /O and |$\rm O^{2+}$| /O fractional abundances throughout the NLR clouds than those derived from pure photoionization models, mainly in shock-dominated objects. This suggests that, in order to minimize the shock effects, the combination of emission-lines emitted by ions with similar intermediate ionization potential could be good metallicity indicators. Finally, we derive two calibrations between the N/O abundance ratio and the N2O2 = log([N  ii ]λ6584/[O  ii ]λ3727) and N2 = log([N  ii ]λ6584/H α) indexes which agree with that derived from pure photoionization models. [ABSTRACT FROM AUTHOR]

We present maps for the electron temperature in the inner kpc of three luminous Seyfert galaxies: Mrk 79, Mrk 348, and Mrk 607 obtained from Gemini Multi-Object Spectrograph-integral field unit observations at spatial resolutions of ∼110–280 pc. We study the distributions of electron temperature in active galaxies and find temperatures varying in the range from ∼8000 to |$\gtrsim 30\, 000\,$| K. Shocks due to gas outflows play an important role in the observed temperature distributions of Mrk 79 and Mrk 348, while standard photoionization models reproduce the derived temperature values for Mrk 607. In Mrk 79 and Mrk 348, we find direct evidence for shock ionization with overall orientation orthogonal to the ionization axis, where shocks can be easily observed as the active galactic nuclei radiation field is shielded by the nuclear dusty torus. This also indicates that even when the ionization cones are narrow, the shocks can be much wider angle. [ABSTRACT FROM AUTHOR]

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 active galactic nuclei (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 abundances of the NLRs were estimated using the theoretical Storchi-Bergmann et al. calibrations, the semi-empirical N2O2 calibration, the Bayesian H  ii-Chi-mistry code and the T e-method. We found that the oxygen abundance estimations via the strong-line methods differ from each other up to ∼0.8 dex, with the largest discrepancies in the low-metallicity regime (⁠|$\rm 12+\log (O/H) \: \lesssim \: 8.5$|⁠). 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. [ABSTRACT FROM AUTHOR]

We present a new methodology for the analysis of the emission lines of the interstellar medium in the narrow-line regions around type-2 active galactic nuclei. Our aim is to provide a recipe that can be used for large samples of objects in a consistent way using different sets of optical emission lines that takes into the account possible variations from the O/H–N/O relation to use [N  ii ] lines. Our approach consists of a bayesian-like comparison between certain observed emission-line ratios sensitive to total oxygen abundance, nitrogen-to-oxygen ratio, and ionization parameter with the predictions from a large grid of photoionization models calculated under the most usual conditions in this environment. We applied our method to a sample of Seyfert 2 galaxies with optical emission-line fluxes and determinations of their chemical properties from detailed models in the literature. Our results agree within the errors with other results and confirm the high metallicity of the objects of the sample, with N/O values consistent with a large secondary production of N, but with a large dispersion. The obtained ionization parameters for this sample are much larger than those for star-forming object at the same metallicity. [ABSTRACT FROM AUTHOR]

Integral field spectroscopy is well known for providing detailed insight of extended sources thanks to the possibility of handling space resolved spectroscopic information. Simple and straightforward analysis such as single line fitting yields interesting results, although it might miss a more complete picture in many cases. Violent star-forming regions, such as starburst galaxies, display very complex emission line profiles due to multiple kinematic components superposed in the line of sight. We perform a spatially resolved kinematical study of a single Green Pea (GP) galaxy, SDSS J083843.63+385350.5, using a new method for analysing integral field unit observations of emission line spectra. The method considers the presence of multiple components in the emission line profiles and makes use of a statistical indicator to determine the meaningful number of components to fit the observed profiles. We are able to identify three distinct kinematic features throughout the field and discuss their link with a rotating component, a strong outflow, and a turbulent mixing layer. We also derive an updated star formation rate for SDSS J0838 and discuss the link between the observed signatures of a large-scale outflow and of the Lyman continuum leakage detected in GP galaxies. [ABSTRACT FROM AUTHOR]

We calculate the effective temperature (T eff) of ionizing star(s), the oxygen abundance of the gas phase |$(\rm O/H)$|⁠, and the ionization parameter U for a sample of H  ii regions located in the discs of 59 spiral galaxies in the redshift range 0.005 < |$z$| < 0.03. We use spectroscopic data taken from the CALIFA data release 3 (DR3) and theoretical (for T eff and U) and empirical (for O/H) calibrations based on strong emission lines. We consider the spatial distribution and radial gradients of these parameters in each galactic disc for the objects in our sample. Most of the galaxies in our sample (∼70 per cent) show positive T eff radial gradients, although some exhibit negative or flat ones. The median value of the T eff radial gradient is 0.762 kK/ R 25. We find that the radial gradients of both log  U and T eff depend on the oxygen abundance gradient, in the sense that the gradient of log  U increases as the |$\log (\rm O/H)$| gradient increases while there is an anti-correlation between the gradient of T eff and the oxygen abundance gradient. Moreover, galaxies with flat oxygen abundance gradients tend to have flat log  U and T eff gradients as well. Although our results are in agreement with the idea of the existence of positive T eff gradients along the disc of the majority of spiral galaxies, it seems that this is not a universal property for these objects. [ABSTRACT FROM AUTHOR]

We built a grid of photoionization models and compiled already available observational emission line intensities ($1000 \,\, \lt \,\, \lambda $ (Å) < 2000) of confirmed star formation regions and Active Galactic Nucleus (AGNs) in order to classify five Lyα emitter (LAE) objects at high redshift (5.7 <  $z$  < 7.2). We selected objects for which at least one metal emission-line was measured. The resulting sample is composed by the objects RXC J2248.7-4431-ID3, HSC J233408+004403, COSY, A1703-zd6, and CR7 (clump C). The photoionization models were built assuming a Power Law (associated with the presence of an AGN), a Direct Collapse Black Hole (DCBH), and Population II stars for the ionizing source. The resulting models were then compared with observational emission-line ratios in six diagnostic diagrams to produce a spectral classification of the sample. We found that CR7 (clump C), HSC J233408+004403 and COSY probably have a non thermal ionizing source (AGN or DCBH) while the RXC J2248.7-4431-ID3 and A1703-zd6 seem to host a stellar cluster. Detailed photoionization models were constructed to reproduce observational emission line ratios of the sample of LAEs, and to derive chemical abundances and number of ionizing photons $Q(\rm H)$ of these objects. From these models, we found metallicities in the range $0.1 \,\, \lesssim \,\, (Z/Z_{\odot }) \,\, \lesssim \,\, 0.5$ and $\log Q(\rm H) \,\, \gt \,\, 53$. Values for C/O abundance ratio derived for the LAEs seem to be consistent with those derived for local star forming objects with similar metallicities, while an overabundance of N/O was found for most of the LAEs. [ABSTRACT FROM AUTHOR]

We present an observational study of the impacts of interactions on the stellar population in a sample of galaxy pairs. Long-slit spectra in the wavelength range 3440-7300 Å obtained with the Gemini Multi-Object Spectrograph (GMOS) at Gemini South for 15 galaxies in nine close pairs were used. The spatial distributions of the stellar population contributions were obtained using the stellar population synthesis code starlight. Taking into account the different contributions to the emitted light, we found that most of the galaxies in our sample are dominated by young/intermediate stellar populations. This result differs from the one derived for isolated galaxies, where the old stellar population dominates the disc surface brightness. We interpreted such different behaviour as being due to the effect of gas inflows along the discs of interacting galaxies on the star formation over a time-scale of the order of about 2 Gyr. We also found that, in general, the secondary galaxy of a pair has a higher contribution from the young stellar population than the primary one. We compared the estimated values of stellar and nebular extinction derived from the synthesis method and the Hα/Hβ emission-line ratio, finding that nebular extinctions are systematically higher than stellar ones by about a factor of 2. We did not find any correlation between nebular and stellar metallicities. Neither did we find a correlation between stellar metallicities and ages, while a positive correlation between nebular metallicities and stellar ages was obtained, with older regions being the most metal-rich. [ABSTRACT FROM AUTHOR]

In this work, we used a grid of photoionization models combined with stellar population synthesis models to derive reliable ionization correction factors (ICFs) for the sulphur in starforming regions. These models cover a large range of nebular parameters and yielding ionic abundances in consonance with those derived through optical and infrared observational data of star-forming regions. From our theoretical ICFs, we suggested an a value of 3.27 ± 0.01 in the classical Stasi'nska formulae. We compared the total sulphur abundance in the gas phase of a large sample of objects by using our theoretical ICF and other approaches. In average, the differences between the determinations via the use of the different ICFs considered are similar to the uncertainties in the S/H estimations. Nevertheless, we noted that for some objects it could reach up to about 0.3 dex for the low-metallicity regime. Despite of the large scatter of the points, we found a trend of S/O ratio to decrease with the metallicity, independently of the ICF used to compute the sulphur total abundance. [ABSTRACT FROM AUTHOR]

In this paper, we derive oxygen abundance gradients from H ii regions located in 11 galaxies in eight systems of close pairs. Long-slit spectra in the range 4400–7300 Å were obtained with the Gemini Multi-Object Spectrograph at Gemini South (GMOS-S). Spatial profiles of oxygen abundance in the gaseous phase along galaxy discs were obtained using calibrations based on strong emission lines (N2 and O3N2). We found oxygen gradients to be significantly flatter for all the studied galaxies than those in typical isolated spiral galaxies. Four objects in our sample, AM 1219A, AM 1256B, AM 2030A and AM 2030B, show a clear break in the oxygen abundance at galactocentric radius R/R25 between 0.2 and 0.5. For AM 1219A and AM 1256B, we found negative slopes for the inner gradients, and for AM 2030B, we found a positive slope. All three cases show a flatter behaviour to the outskirts of the galaxies. For AM 2030A, we found a positive slope for the outer gradient, while the inner gradient is almost compatible with a flat behaviour. We found a decrease of star formation efficiency in the zone that corresponds to the oxygen abundance gradient break for AM 1219A and AM 2030B. For the former, a minimum in the estimated metallicities was found very close to the break zone, which could be associated with a corotation radius. However, AM 1256B and AM 2030A, present a star formation rate maximum but not an extreme oxygen abundance value. All four interacting systems that show oxygen gradient breaks have extreme SFR values located very close to break zones.The H ii regions located in close pairs of galaxies follow the same relation between the ionization parameter and the oxygen abundance as those regions in isolated galaxies. [ABSTRACT FROM AUTHOR]