Repositório DSpace :: Navegando por Assunto "Galaxies: active"

Navegando por Assunto "Galaxies: active"

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Chemical abundances in Seyfert galaxies – IX. Helium abundance estimates
(Royal Astronomical Society) Dors Junior, Oli Luiz; Valerdi, Mabel; Lemes, Priscila Freitas; Krabbe, Angela Cristina; Riffel, Rogemar André; Amôres, Eduardo Brescansin; Riffel, Rogério; Armah, Mark; Monteiro, Adriano Francisco; Oliveira Junior, Celso Benedito de
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 < λ(Å) < 7000] of 65 local Seyfert 2 nuclei (z < 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 oversolar 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
Chemical abundances in Seyfert galaxies – V. The discovery of shocked emission outside the AGN ionization axis
(Royal Astronomical Society) Riffel, Rogemar André; Dors Júnior, Oli Luiz; Armah, Mark; Bergmann, Thaisa Storchi; Feltre, Anna; Hägele, Guilhermo Frederico; Cardaci, Mónica Viviana; Dutra, Daniel Ruschel; Krabbe, Angela Cristina; Pérez-Montero, Enrique; Zakamska, Nadia L.; Freitas, Izabel C.
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 > 30000 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.
Chemical abundances in Seyfert galaxies – VI. Empirical abundance calibration
(Royal Astronomical Society) Dors Júnior, Oli Luiz
We derived a bi-dimensional calibration between the emission-line ratios R23 =([OII]λ3726+λ3729+[OIII]λ4959+ λ5007)/H β , P = [([O III] λ4959 + λ5007)/H β ]/R23 and the oxygen abundance relative to hydrogen (O/H) in the gas phase of Seyfert 1 and 2 nuclei. In view of this, emission-line intensity ratios for a sample of objects taken from the Sloan Digital Sky Survey Data Release 7 measured by the MPA/JHU group and direct estimates of O/H based on Te-method, adapted for active galactic nuclei (AGNs), are considered. We find no variation of R23 observed along the radii of AGNs, which shows that this line ratio is a good oxygen abundance (O/H) indicator for the class of objects considered in this work. The derived O/H = f(R23, P) relation produces O/H values similar to estimations via Te-method in a wide range of metallicities [8.0 < 12 + log (O/H) < 9.2]. Conversely to star-forming regions in the high-metallicity regime, R23 shows a positive correlation trend with O/H in AGNs. This indicates that the hardness of ionizing radiation is not affected by the metallicities in these objects or narrow-line regions are not significantly modified by changes in the spectral energy distribution due to metallicity variations.
Chemical abundances in Seyfert galaxies – VII. Direct abundance determination of neon based on optical and infrared emission lines
(Royal Astronomical Society) Armah, Mark; Dors Júnior, Oli Luiz; Aydar, Catarina Pasta; Cardaci, Mónica Viviana; Hägele, Guilhermo Frederico; Feltre, Anna; Riffel, Rogério; Riffel, Rogemar André; Krabbe, Angela Cristina
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 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 [te(Ne 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 te(Ne iii) is considered. We propose a semi-empirical Ionization Correction Factor (ICF) for the neon, based on [Ne II]12.81μm, [Ne III]15.56μm, 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. [12 + log(O/H) 8.80]) an increase in Ne/O with O/H is found, which likely indicates secondary stellar production for the neon.
Chemical abundances in Seyfert galaxies – VIII. Argon abundance estimates
(Royal Astronomical Society) Monteiro, Adriano Francisco; Dors Júnior, Oli Luiz
For the first time, the argon abundance relative to hydrogen abundance (Ar/H) in the narrow line region of a sample of Seyfert 2 nuclei has been derived. In view of this, optical narrow emission line intensities of a sample of 64 local Seyfert 2 nuclei (z < 0.25) taken from Sloan Digital Sky Survey DR7 and measured by the MPA/JHU group were considered. We adopted the Te-method for AGNs, which is based on direct determination of the electron temperature, together with a grid of photoionization model results, built with the CLOUDY code, to obtain a method for the derivation of the Ar/H abundance. We find that for a metallicity range of 0.2 (Z/Z) 2.0, Seyfert 2 nuclei present Ar/H abundance ranging from ∼0.1 to ∼3 times the argon solar value, adopting log(O/H) = −3.31 and log(Ar/H) = −5.60. These range of values correspond to 8.0 (12 + log(O/H) 9.0 and 5.4 (12 + log(Ar/H) 6.9, respectively. The range of Ar/H and Ar/O abundance values obtained from our sample are in consonance with estimations from extrapolations of the radial abundance gradients to the central parts of the disc for four spiral galaxies. We combined our abundance results with estimates obtained from a sample of H II galaxies, which were taken from the literature, and found that the Ar/O abundance ratio decreases slightly as the O/H abundance increases.
Constraints on the densities and temperature of the Seyfert 2 narrow line region
(EDP Sciences) Binette, Luc; Martin, Montserrat Villar; Dors Junior, Oli Luiz; Krongold, Yair; Morisset, Christophe; Revalski, Mitchell; Alarie, Alexandre; Riffel, Rogemar André; Dopita, Michael
Context. Different studies have reported the so-called temperature problem of the narrow line region (NLR) of active galactic nuclei (AGNs). Its origin is still an open issue. To properly address its cause, a trustworthy temperature indicator is required. Aims. To determine the temperature of an emission line plasma, the [O iii] (λ4363Å/λ5007Å) line ratio is typically used. However, in the case of the NLR of AGNs, this ratio is not reliable when the electron density extends much above 10 cm−3 as collisional deexcitation strongly affects this ratio independently of the temperature. To verify the density regime, we need a density diagnostic that applies to high excitation plasma. Methods. We propose that the weak [Ar iv] λλ4711,40Å doublet is the appropriate tool for evaluating the density of the high excitation plasma. We subsequently made use of the recent S7 survey sample to extract reliable measurements of the weak [Ar iv] doublet in 16 high excitation Seyfert 2s. As a result we could derive the plasma density of the NLR of our Seyfert 2 sample and compared the temperature inferred from the observed [O iii] (λ4363Å/λ5007Å) ratios. Results. It was found that 13 Seyfert 2s cluster near similar values as the [O iii] (λ4363Å/λ5007Å) ratio, at a mean value of 0.0146 ± 0.0020. Three objects labeled outliers stand out at markedly higher [O iii] values (>0.03). Conclusions. If for each object one assumes a single density, the values inferred from the [Ar iv] doublet for the 13 clustering objects all lie below 60 000 cm−3 , indicating that the [O iii] (λ4363Å/λ5007Å) ratios in these objects is a valid tracer of plasma temperature. Even when assuming a continuous power-law distribution of the density, the inferred cut-off density required to reproduce the observed 5.1 −3 [Ar iv] doublet is in all cases <10 cm. The average NLR temperature inferred for the 13 Seyfert 2s is 13 000 ± 703 K, which photoionization models have difficulty reproducing. Subsequently we considered different mechanisms to account for the observed [O iii] ratios. For the three outliers, a double-bump density distribution is likely required, with the densest component having a density >10 cm-3 .
Cosmic metallicity evolution of Active Galactic Nuclei: implications for optical diagnostic diagrams
(Royal Astronomical Society) Dors Junior, Oli Luiz; Cardaci, Mónica Viviana; Hägele, Guilhermo Frederico; Ilha, Gabriele da Silva; Oliveira Junior, Celso Benedito de; Riffel, Rogemar André; 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.
Electron temperature fluctuations in Seyfert galaxies
(Royal Astronomical Society) Riffel, Rogemar André; Dors Júnior, Oli Luiz; Krabbe, Angela Cristina; Esteban, César
We use Gemini GMOS-IFU observations of three luminous nearby Seyfert galaxies (Mrk 79, Mrk 348, and Mrk 607) to estimate the electron temperature (Te) fluctuations in the inner 0.4–1.1 kpc region of these galaxies. Based on Te determinations throug the [O III]λ5007/λ4363 emission line ratio of each spaxel, temperature variations are quantified by computing the integrated value of the temperature fluctuation parameter (t 2) projected in the plane of the sky t 2 A, for the first time in active galactic nuclei (AGNs). We find t 2 A values of 0.135, 0.039, and 0.015 for Mrk 79, Mrk 348, and Mrk 607, respectively, which are of the same order or larger than the maximum values reported in star-forming regions and planetary nebulae. Taking into account that t 2 A should be considered a lower limit of the total t 2 in the nebular volume, the results suggest that the impact of such fluctuations on chemical abundance determinations can be important in some AGNs.
Gas-phase metallicity determinations in nearby AGNs with SDSS-IV MaNGA: evidence of metal-poor accretion
(Royal Astronomical Society) Nascimento, Janaína Correa do; Dors Junior, Oli Luiz; Bergmann, Thaisa Storchi; Mallmann, Nícolas Dullius; Riffel, Rogério; Ilha, Gabriele da Silva; Riffel, Rogemar André; Rembold, Sandro Barboza; Deconto-Machado, Alice; Costa, Luiz N. da; Armah, Mark
We derive the metallicity (traced by the O/H abundance) of the narrow-line region (NLR) of 108 Seyfert galaxies as well as radial metallicity gradients along their galaxy discs and of these of a matched control sample of no active galaxies. In view of that, observational data from the SDSS-IV MaNGA survey and strong emission-line calibrations taken from the literature were considered. The metallicity obtained for the NLRs was compared to the value derived from the extrapolation of the radial oxygen abundance gradient, obtained from H II region estimates along the galaxy disc, to the central part of the host galaxies. We find that, for most of the objects (∼ 80 per cent), the NLR metallicity is lower than the extrapolated value, with the average difference (D ) between these estimates ranging from 0.16 to 0.30 dex. We suggest that D is due to the accretion of metal-poor gas to the AGN that feeds the nuclear supermassive black hole (SMBH), which is drawn from a reservoir molecular and/or neutral hydrogen around the SMBH. Additionally, we look for correlations between D and the electron density (Ne), [O III]λ5007, and H α luminosities, extinction coefficient (AV) of the NLRs, as well as the stellar mass (M∗) of the host galaxies. Evidence of an inverse correlation between the D and the parameters Ne, M∗, and Av was found.
Optical and mid-infrared line emission in nearby Seyfert galaxies
(EDP Sciences) Feltre, Anna; Gruppioni, Carlotta; Marchetti, Lucia; Mahoro, Antoine; Salvestrini, Francesco; Mignoli, Marco; Bisigello, Laura; Calura, Francesco; Charlot, Stephane; Chevallard, Jacopo; Romero-Colmenero, Encarni; Curtis-Lake, Emma; Delvecchio, Ivan; Dors Junior, Oli Luiz; Hirschmann, Michaela; Jarrett, Thomas; Moloko, Malebo E.; Plat, Adèle; Pozzi, F.; Sefako, Ramotholo; Traina, A.; Vaccari, Mattia; Väisänen, Pauli; Vallini, Livia; Vidal-García, Alba; Vignali, Cristian
Line ratio diagnostics provide valuable clues as to the source of ionizing radiation in galaxies with intense black hole accretion and starbursting events, such as local Seyfert galaxies or galaxies at the peak of their star formation history. We aim to provide a reference joint optical and mid-IR line ratio analysis for studying active galactic nucleus (AGN) identification via line-ratio diagnostics and testing predictions from photoionization models. We first obtained homogenous optical spectra with the Southern Africa Large Telescope for 42 Seyfert galaxies with available Spitzer/IRS spectroscopy, along with X-ray to mid-IR multiband data. After confirming the power of the main optical ([O III]λ5007) and mid-IR ([Ne V]14.3 μm, [O IV]25.9 μm, [Ne III]15.7 μm) emission lines in tracing AGN activity, we explored diagrams based on ratios of optical and mid-IR lines by exploiting photoionization models of different ionizing sources (AGN, star formation, and shocks). We find that pure AGN photoionization models are good at reproducing observations of Seyfert galaxies with an AGN fractional contribution to the mid-IR (5 − 40 μm) continuum emission larger than 50 per cent. For targets with a lower AGN contribution, even assuming a hard ionizing field from the central accretion disk (Fν ∝ να, with α ≈ −0.9), these same models do not fully reproduce the observed mid-IR line ratios. Mid-IR line ratios such as [Ne V]14.3 μm/[Ne II]12.8 μm, [O IV]25.9 μm/[Ne II]12.8 μm, and [Ne III]15.7 μm/[Ne II]12.8 μm show a dependence on the AGN fractional contribution to the mid-IR, unlike optical line ratios. An additional source of ionization, either from star formation or radiative shocks, can help explain the observations in the mid-IR. While mid-IR line ratios are good tracers of the AGN activity versus star formation, among the combinations of optical and mid-IR diagnostics in line-ratio diagrams, only those involving the [O I]/Hα ratio are promising diagnostics for simultaneously unraveling the relative roles of AGN, star formation, and shocks. A proper identification of the dominant source of ionizing photons would require the exploitation of analysis tools based on advanced statistical techniques as well as spatially resolved data.
Oxygen abundances in the narrow line regions of Seyfert galaxies and the metallicity–luminosity relation
(Royal Astronomical Society) Armah, Mark; Riffel, Rogério; Dors Junior, Oli Luiz; Oh, Kyuseok; Koss, Michael J.; Ricci, Claudio; Trakhtenbrot, Benny; Valerdi, Mabel; Riffel, Rogemar André; Krabbe, Angela Cristina
We present oxygen abundances relative to hydrogen (O/H) in the narrow line regions (NLRs) gas phases of Seyferts 1 (Sy 1s) and Seyferts 2 (Sy 2s) active galactic nuclei (AGNs). We used fluxes of the optical narrow emission line intensities [Å] of 561 Seyfert nuclei in the local Universe ( z ≲ 0.31) from the second catalogue and data release (DR2) of the BAT AGN Spectroscopic Survey, which focuses on the Swift-BAT hard X-ray (≳ 10 keV) detected AGNs. We derived O/H from relative intensities of the emission lines via the strong-line methods. We find that the AGN O/H abundances are related to their hosts stellar masses and that they follow a downward redshift evolution. The derived O/H together with the hard X-ray luminosity (LX) were used to study the X-ray luminosity–metallicity (LX–ZNLR) relation for the first time in Seyfert galaxies. In contrast to the broad-line focused (LX–ZBLR) studies, we find that the LX–ZNLR exhibit significant anticorrelations with the Eddington ratio (λEdd) and these correlations vary with redshifts. This result indicates that the low-luminous AGNs are more actively undergoing interstellar medium enrichment through star formation in comparison with the more luminous X-ray sources. Our results suggest that the AGN is somehow driving the galaxy chemical enrichment, as a result of the inflow of pristine gas that is diluting the metal rich gas, together with a recent cessation on the circumnuclear star-formation.

Navegando por Assunto "Galaxies: active"

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