46 research outputs found
A new tool to derive chemical abundances in Type-2 Active Galactic Nuclei
We present a new tool for the analysis of the optical emission lines of the
gas in the Narrow Line Region (NLR) around Active Galactic Nuclei (AGNs). This
new tool can be used in large samples of objects in a consistent way using
different sets of optical emission-lines taking into the account possible
variations from the O/H - N/O relation. The code compares certain observed
emission-line ratios with the predictions from a large grid of photoionization
models calculated under the most usual conditions in the NLR of AGNs to
calculate the total oxygen abundance, nitrogen-to-oxygen ratio and ionization
parameter. We applied our method to a sample of Seyfert 2 galaxies with optical
emission-line fluxes from the literature. Our results confirm the high
metallicity of the objects of the sample and provide consistent values with the
direct method. The usage of models to calculate precise ICFs is mandatory when
only optical emission lines are available to derive chemical abundances using
the direct method in NLRs of AGN.Comment: Proceedings paper of the IAU symposium "Nuclear Activity in Galaxies
Across Cosmic Time" (Ethiopia) accepted to be published under the Cambridge
University Press, eds. M. Povi\'c, P. Marziani, J. Masegosa, H. Netzer, S. H.
Negu, and S. B. Tessem
On the central abundances of Active Galactic Nuclei and Star-forming Galaxies
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 (the theoretical calibration of Storchi-Bergmann et al. 1998), via the direct Te-method, and the central intersect abundances in the host galax- ies determined from the radial abundance gradients. We found that the Te-method underestimates the oxygen abundances by up to âŒ2 dex (with average value of ~0.8 dex) compared to the abundances derived through the strong-line method. This con- firms 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 abun- dances 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 at- tainable abundance in galaxies (~2 times the solar value). This suggests that there is no extraordinary chemical enrichment of the NLRs of AGNs.Fil: Dors Jr., O. L.. Universidade Do Vale Do ParaĂba; BrasilFil: Cardaci, Monica Viviana. Universidad Nacional de la Plata. Facultad de Ciencias AstronĂłmicas y GeofĂsicas; Argentina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico La Plata. Instituto de AstrofĂsica de La Plata; ArgentinaFil: HĂ€gele, Guillermo Federico. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico la Plata. Instituto de AstrofĂsica de la Plata; Argentina. Universidad Nacional de la Plata. Facultad de Ciencias AstronĂłmicas y GeofĂsicas; ArgentinaFil: Rodrigues, I.. Universidade Do Vale Do ParaĂba; BrasilFil: Grebel, E. K. . UniversitĂ€t Heidelberg. Astronomisches Rechen-Institut. Zentrum fĂŒr Astronomie; AlemaniaFil: Pilyugin, L. S. . UniversitĂ€t Heidelberg; Alemania. National Academy of Sciences of Ukraine; Ucrania. Kazan Federal University; RusiaFil: Freitas Lemes, P. . Universidade Do Vale Do ParaĂba; BrasilFil: Krabbe, A. C. . Universidade Do Vale Do ParaĂba; Brasi
On the central abundances of Active Galactic Nuclei and Star-forming Galaxies
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 (the theoretical calibration of Storchi-Bergmann et al. 1998), 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 âŒ2 dex (with average value of ~0.8 dex) compared to the abundances derived through the strong-line method. This con- firms 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 abun- dances 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 at- tainable abundance in galaxies (~2 times the solar value). This suggests that there is no extraordinary chemical enrichment of the NLRs of AGNs.Facultad de Ciencias AstronĂłmicas y GeofĂsicasInstituto de AstrofĂsica de La Plat
Chemical abundances of Seyfert 2 AGNs, II: N2 metallicity calibration based on SDSS
We present a semi-empirical calibration between the metallicity (Z) of Seyfert 2 active galactic nuclei and the N2 = log([N II]λ6584/H a) emission-line intensity ratio. This calibration was derived through the [OIII]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 †0.4) taken from the Sloan Digital Sky Survey DR7 data set. The obtained Z-N2 relation is valid for the range 0.3 †(Z/Zâ) †2.0 that corresponds to -0.7 †(N2) †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 [OIII]/[O II] line ratio, almost independent of other nebular parameter, was obtained.Fil: Carvalho, S.P.. Universidade Do Vale Do Paraiba; BrasilFil: Dors, O. L.. Universidade Do Vale Do Paraiba; BrasilFil: Cardaci, Monica Viviana. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - La Plata. Instituto de AstrofĂsica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias AstronĂłmicas y GeofĂsicas. Instituto de AstrofĂsica La Plata; ArgentinaFil: HĂ€gele, Guillermo Federico. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - La Plata. Instituto de AstrofĂsica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias AstronĂłmicas y GeofĂsicas. Instituto de AstrofĂsica La Plata; ArgentinaFil: Krabbe, Nora Cristina. Universidade Do Vale Do Paraiba; BrasilFil: PĂ©rez Montero, E.. Instituto de AstrofĂsica de AndalucĂa; EspañaFil: Monteiro, A.F.. Universidade Do Vale Do Paraiba; BrasilFil: Armah, M.. Universidade Do Vale Do Paraiba; BrasilFil: Freitas Lemes, P.. Universidade Do Vale Do Paraiba; Brasi
On the central abundances of Active Galactic Nuclei and Star-forming Galaxies
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 (the theoretical calibration of Storchi-Bergmann et al. 1998), 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 âŒ2 dex (with average value of ~0.8 dex) compared to the abundances derived through the strong-line method. This con- firms 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 abun- dances 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 at- tainable abundance in galaxies (~2 times the solar value). This suggests that there is no extraordinary chemical enrichment of the NLRs of AGNs.Facultad de Ciencias AstronĂłmicas y GeofĂsicasInstituto de AstrofĂsica de La Plat
Gemini GMOS spectroscopy of HeII nebulae in M33
We have carried out a narrow-band survey of the Local Group galaxy, M33, in
the HeII4686 emission line, to identify HeII nebulae in this galaxy. With
spectroscopic follow-up observations, we confirm three of seven candidate
objects, including identification of two new HeII nebulae, BCLMP651, HBW673. We
also obtain spectra of associated ionizing stars for all the HII regions,
identifying two new WN stars. We demonstrate that the ionizing source for the
known HeII nebula, MA 1, is consistent with being the early-type WN star MC8
(M33-WR14), by carrying out a combined stellar and nebular analysis of MC8 and
MA1. We were unable to identify the helium ionizing sources for HBW 673 and
BCLMP 651, which do not appear to be Wolf-Rayet stars. According to the
[OIII]5007/Hbeta vs [NII]6584/Halpha diagnostic diagram, excitation mechanisms
apart from hot stellar continuum are needed to account for the nebular emission
in HBW 673, which appears to have no stellar source at all.Comment: Accepted for publication in Astronomy and Astrophysics. 22 pages, 10
figure
Spintronics: Fundamentals and applications
Spintronics, or spin electronics, involves the study of active control and
manipulation of spin degrees of freedom in solid-state systems. This article
reviews the current status of this subject, including both recent advances and
well-established results. The primary focus is on the basic physical principles
underlying the generation of carrier spin polarization, spin dynamics, and
spin-polarized transport in semiconductors and metals. Spin transport differs
from charge transport in that spin is a nonconserved quantity in solids due to
spin-orbit and hyperfine coupling. The authors discuss in detail spin
decoherence mechanisms in metals and semiconductors. Various theories of spin
injection and spin-polarized transport are applied to hybrid structures
relevant to spin-based devices and fundamental studies of materials properties.
Experimental work is reviewed with the emphasis on projected applications, in
which external electric and magnetic fields and illumination by light will be
used to control spin and charge dynamics to create new functionalities not
feasible or ineffective with conventional electronics.Comment: invited review, 36 figures, 900+ references; minor stylistic changes
from the published versio
The effect of nutrients on pyrrolizidine alkaloids in Senecio plants and their interactions with herbivores and pathogens
The aim of this review is to combine the knowledge of studies on effects of nutrients on pyrrolizidine alkaloids (PAs) in Senecio with those studies of effects of PAs on herbivores and pathogens in order to predict the effects that nutrients may have on herbivores and pathogens via changes in PAs. We discuss whether these predictions match with the outcome of studies where the effect of nutrients on herbivores and insects were measured. PA concentrations in S. jacobaea, S. vulgaris and S. aquaticus were mostly reduced by NPK fertilization, with genotype-specific effects occurring. Plant organs varied in their response to increased fertilization; PA concentrations in flowers remained constant, while shoot and roots were mostly negatively affected. Biomass change is probably largely responsible for the change in concentrations. Nutrients affect both the variety and the levels of PAs in the plant. The reduced PA concentrations after NPK fertilization was expected to benefit herbivores, but no or negative responses from insect herbivores were observed. Apparently other changes in the plant after fertilization are overriding the effect of PAs. Pathogens do seem to benefit from the lower PA concentrations after fertilization; they were more detrimental to fertilized plants than to unfertilized control plants. Future studies should include the effect of each element of nutrients separately and in combinations in order to gain more insight in the effect of specific nutrients on PA content in Senecio plants