ABSTRACT
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
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
We present a semi-empirical calibration between the metallicity (Z) of Seyfert 2 active galactic nuclei and the N2 = log(N iiλ6584/H α) emission-line intensity ratio. This calibration was ...derived through the O iiiλ5007/O iiλ3727 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
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 (Te-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 (t2) and high (t3) ionization gas zones derived for H ii regions in AGN chemical abundance studies. Using a photoionization model grid, we derived a new expression for t2 as a function of t3 valid for Seyfert 2 nuclei. The use of this new expression in the AGN estimation of the O/H abundances based on Te-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 Te-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
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 ...(Te-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 Te-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 Te-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 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
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
For the first time, neon abundance has been derived in the narrow line region from a sample of Seyfert 2 nuclei. In view of this, we compiled from the literature fluxes of optical and ...infrared (IR) narrow emission lines for 35 Seyfert 2 nuclei in the local universe ($z \:\lesssim \:0.06$). The relative intensities of emission lines were used to derive the ionic and total neon and oxygen abundances through electron temperature estimations (Te-method). For the neon, abundance estimates were obtained by using both Te-method and IR-method. Based on photoionization model results, we found a lower electron temperature $t_{\rm e}({\rm Ne\, \small {III}})$ for the gas phase where the Ne2 + is located in comparison with t3 for the O2 + ion. We find that the differences (D) between Ne2 +/H+ ionic abundances calculated from IR-method and Te-method (assuming t3 in the Ne2 +/H+ derivation) are similar to the derivations in star-forming regions (SFs) and they are reduced by a mean factor of ∼3 when $t_{\rm e}({\rm Ne\, \small {III}})$ is considered. We propose a semi-empirical Ionization Correction Factor (ICF) for the neon, based on Ne ii12.81$\rm{\mu m}$, Ne iii15.56$\rm{\mu m}$, and oxygen ionic abundance ratios. We find that the average Ne/H abundance for the Seyfert 2s sample is nearly 2 times higher than similar estimate for SFs. Finally, for the very high metallicity regime (i.e. $\rm 12+log(O/H)\: \gtrsim \: 8.80$) an increase in Ne/O with O/H is found, which likely indicates secondary stellar production for the neon.
ABSTRACT
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.
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