Navegando por Autor "Feltre, Anna"

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    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.
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    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.
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    Chemical abundances in Seyfert galaxies – X. Sulphur abundance estimates
    (Royal Astronomical Society) Dors Junior, Oli Luiz; Valerdi, Mabel; Riffel, Rogemar André; Riffel, Rogério; Cardaci, Mónica Viviana; Hägele, Guilhermo Frederico; Armah, Mark; Revalski, Mitchell; Flury, Sophia; Lemes, Priscila Freitas; Amôres, Eduardo; Krabbe, Angela Cristina; Binette, Luc; Feltre, Anna; Bergmann, Thaisa Storchi
    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 S+ ions are located in comparison with that of star-forming regions (SFs). However, Sy 2s present higher temperature values (∼10 000 K) in the region where most of the S2+ ions are located relative to that of SFs. We derive the total sulphur abundance in the range of 6.2 􏰀 12 + log(S/H) 􏰀 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 [12 + log(O/H) 􏰁 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.
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    Doubly ionized neon ionic abundance of seyfert 2 nuclei based on infrared and optical emission lines
    (2020-10-19) Dors Junior, Oli Luiz; Krabbe, Angela Cristina; Hagelle, Guillermo Frederico; Feltre, Anna; Armah, Mark; São José dos Campos
    One of the most reliable method to determine the chemical abundance of heavy elements in gaseous nebulae is the (tau)e-method, which is based on the measurements of auroral emission lines (e.g., [O III] (lambda)4363 Å). However, this method yields unreal and subsolar abundances in AGNs. This phenomenon is customarily referred to as “temperature problem”, and its origin is an open question in nebular astrophysics. Comparison between optical and infrared abundances can be used to obtain the level of electron temperature fluctuations in AGNs, generally attributed to the origin of the temperature problem. In this work, optical and infrared emission-line intensities of neon from a sample of 36 Seyfert 2 nuclei compiled from the literature and used to calculate the ionic abundance of the neon twice ionized in relation to the hydrogen one ion (Ne2+/H+). This methodology makes it possible to obtain the level of electron temperature fluctuation necessary to conciliate the optical and infrared abundance values. We investigated the use of the Balmer decrement observed ratio of intensities of the 3 (seta) 2 (H(alfa) (lambda)6563 Å) and 4 (seta) 2 (H(beta) (lambda)4861 Å) transitions of the hydrogen atom compared to their intrinsic intensity ratio so as to yield a relative extinction in the Narrow Line Region (NLR) of Seyfert 2 nuclei and find that the use of (iota)(H(alfa)/H(beta)) = 2.85 gives (tau)e values of 700 ± 30 K higher than the (tau)e values derived from (iota)(H(alfa)/H(beta)) = 3.10. Our analysis show that, differences (D) between abundance values from optical and infrared lines range from 0.1334 ± 0.0219 to 2.0636 ± 0.0151 dex, with an averaged value of 0.6931 ± 0.0052 dex. This averaged value is approximately ~ 0.01 ± 0.01 dex higher than the one derived in H ii regions studies. We did not find any relation between the ionic abundance difference (D) and the ionization parameter (U), which implies D is independent from U. We estimated the level of temperature fluctuation in terms of the t2 parameter in the range from 0.0006 to 0.4365 ± 0.0053 with an average value of 0.1859 ± 0.0011. We conclude that, if electron temperature fluctuations are present in AGNs, they are somewhat more significant than in H ii regions.
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    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.