Navegando por Assunto "Galaxies"

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    AGN feedback and star formation in the peculiar galaxy NGC 232: insights from VLT-MUSE observations
    (Royal Astronomical Society) Souza, José Henrique Costa; Riffel, Rogemar André; Dors Junior, Oli Luiz; Riffel, Rogério; Poppe, Paulo César da Rocha
    We use VLT-MUSE integral field unit data to study the ionized gas physical properties and kinematics as well as the stellar populations of the Seyfert 2 galaxy NGC 232 as an opportunity to understand the role of AGN feedback on star formation. The data cover a field of view of 60 × 60 arcsec2 at a spatial resolution of ∼850 pc. The emission-line profiles have been fitted with two Gaussian components, one associated to the emission of the gas in the disc and the other due to a bi-conical outflow. The spectral synthesis suggests a predominantly old stellar population with ages exceeding 2 Gyr, with the largest contributions seen at the nucleus and decreasing outwards. Meanwhile, the young and intermediate age stellar populations exhibit a positive gradient with increasing radius and a circum-nuclear star-forming ring with radius of ∼0.5 kpc traced by stars younger than 20 Myr, is observed. This, along with the fact that AGN and SF dominated regions present similar gaseous oxygen abundances, suggests a shared reservoir feeding both star formation and the AGN. We have estimated a maximum outflow rate in ionized gas of ∼1.26 M yr−1 observed at a distance of ∼560 pc from the nucleus. The corresponding maximum kinetic power of the outflow is ∼3.4 × 1041 erg s−1. This released energy could be sufficient to suppress star formation within the ionization cone, as evidenced by the lower star formation rates observed in this region.
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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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    Chemical abundances of LINER galaxies – nitrogen abundance estimations
    (Royal Astronomical Society) Oliveira Junior, Celso Benedito de ; Krabbe, Angela Cristina; Dors Junior, Oli Luiz; Zinchenko, Igor; Hernandez-Jimenez, José Andrés; Cardaci, Mónica Viviana; Hägele, Guilhermo Frederico; Ilha, Gabriele da Silva
    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 8.0 􏰀 12 + log(O/H) 􏰀 9.0 (mean value 8.74 ± 0.27) and 7.6 􏰀 12 + log(N/H) 􏰀 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.
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    Ionized gas outflows and shock-heated emission in the highly inclined active galaxy CGCG 012-070
    (Royal Astronomical Society) Vieira, Lucas Ramos; Riffel, Rogemar André; Riffel, Rogério; Dors Junior, Oli Luiz; Bianchin, Marina; Storchi-Bergmann, Thaisa
    Active galactic nuclei (AGNs) exhibit excess mid-infrared H2 emission compared to star-forming galaxies, likely driven by outflows and shocks inferred from integrated spectra. We present optical IFU (integral field unit) observations of the central 2 kpc of the AGN host CGCG 012-070, selected for its pronounced H2 emission excess, to map stellar and gas kinematics. The stellar velocity field is well described by a rotating disc with a line of nodes at 103◦ ± 4◦, with the north-west side approaching and the southeast side receding. Gas kinematics, traced by strong emission lines, show two components: a narrow one (σ 􏰁 200 km s−1 ) in the disc plane following stellar motions, and a broad (σ 􏰂 300 km s−1 ) associated with outflows within the inner ∼1 kpc. Disc gas emission is mainly driven by AGN photoionization, while the outflow also includes shock-heated gas, as indicated by flux ratio diagnostics. The outflows are radiatively driven, with a mass-outflow rate of (0.067 ± 0.026) M⊙ yr−1 and a kinetic coupling efficiency of 0.07 per cent, potentially redistributing gas and contributing to maintenance-mode feedback in CGCG 012-070. Our results provide further evidence that the warm H2 emission excess in nearby AGN is associated with shocks produced by outflows. Observations of other gas phases, such as cold molecular gas, are necessary to gain a more comprehensive understanding of the impact of the outflows on the host galaxy.
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    Metallicity of active galactic nuclei from ultraviolet and optical emission lines - II. Revisiting the C43 metallicity calibration and its implications
    (Oxford) Dors Junior, Oli Luiz; Oliveira, Celso Benedito de; Cardaci, Mónica Viviana; Hägele, Guillermo Federico; Armah, Mark; Riffel, Rogemar André; Vieira, Lucas Ramos; Almeida, Gleicy Caroline de; Morais, Istenio Nunes de; Santos, Pedro Camargo
    In this study, a new semi-empirical calibration is proposed between ultraviolet emission lines (CIII]λ1909, CIVλ1549, HeII]λ1640) of type 2 active galactic nuclei (AGNs) and their metallicity (Z). This calibration is derived by comparing a large sample of 106 objects (data taken from the literature) located over a wide range of redshifts (0 􏰁 z 􏰁 4.0) with predictions from photoionization models that adopt a recent C/O–O/H relation derived via estimates using the Te method, which is considered the most reliable method. We found that the new calibration produces Z values in agreement (within an uncertainty of ±0.1 dex) with those from other calibrations and from estimates via the Te-method. We find also that AGN metallicities are already high at early epochs, with no evidence for monotonic evolution across the redshift range 0 􏰁 z 􏰁 12. Notably, the highest metallicities in our sample, reaching up to 4 Z⊙, are found in objects at 2 􏰁 z 􏰁 3. This redshift range coincides with the peak of the cosmic star formation rate history, suggesting a strong connection between the major epoch of star formation, black hole growth, and rapid metal enrichment in the host galaxies of AGNs. Furthermore, our analysis reveals no significant correlation between AGN metallicity and radio properties (radio spectral index or radio luminosity) or host galaxy stellar mass. The lack of a clear mass–metallicity relation, consistent with findings for local AGNs, suggests that the chemical evolution of the nuclear gas is decoupled from the global properties of the host galaxy.
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    Metallicity of active galactic nuclei from ultraviolet and optical emission lines: I. Carbon abundance dependence
    (Royal Astronomical Society) Dors Junior, Oli Luiz; Oliveira Junior, Celso Benedito de; Cardaci, Mónica Viviana; Hagele, Guillermo Federico; Morais, Istenio Nunes de; Ji, Xihan; Riffel, Rogemar André; Riffel, Rogério; Mezcua, Mar; Almeida, Gleicy Caroline de; Santos, Pedro Camargo; Mellos, Maitê Silvana de Zorzi de
    Metallicity (Z) estimates based on ultraviolet (UV) emission lines from the narrow-line regions of active galactic nuclei (AGNs) have been found to differ from those derived from optical lines. However, the origin of this discrepancy (ZR) remains poorly understood. To investigate the source of ZR, we compiled from the literature the fluxes of narrow near- UV [1000 < λ(Å) < 2000] and optical [3000 < λ(Å) < 7000] emission-line measurements for a sample of 11 AGNs (nine at z < 0.4 and two at z ∼ 2.4). Metallicity values for our sample were derived using a semi-empirical calibration based on the C43 = log[(C IVλ1549 + C III]λ1909)/He IIλ1640] emission-line ratio and compared with those obtained via direct measurement of the electron temperature (Te-method) and via calibrations based on optical emission lines. The source of the discrepancy was investigated in terms of the ionization parameter (U), electron density (Ne), and carbon abundance (C/H). We found a weak correlation between ZR, U, and Ne. However, a moderate correlation was observed between ZR and direct estimates of C/H, suggesting that the previously assumed (C/O)–Z relations in photoionization models used to derive UV carbon-line calibrations may not be valid for AGNs. By combining a large set of abundance estimates for local star-forming regions with those of our AGN sample, we derived a new (C/O)–Z relation. Comparisons between the results of photoionization models that assume this new abundance relation and the UV observational data of our sample produce Z values derived from the C43 index that are consistent with those obtained using the Te-method.