scholarly journals The Excitation Mechanism of Emission‐Line Regions in Seyfert Galaxies

1999 ◽  
Vol 521 (2) ◽  
pp. 531-546 ◽  
Author(s):  
Ian Evans ◽  
Anuradha Koratkar ◽  
Mark Allen ◽  
Michael Dopita ◽  
Zlatan Tsvetanov
Keyword(s):  
Emission Line ◽  
Seyfert Galaxies ◽  
Excitation Mechanism

scholarly journals Excitation Mechanisms in Seyfert Galaxies

1997 ◽  
Vol 159 ◽  
pp. 392-393
Author(s):  
M.G. Allen ◽  
M.A. Dopita ◽  
Z. I. Tsvetanov
Keyword(s):  
Emission Line ◽  
Spatial Dependence ◽  
Seyfert Galaxies ◽  
Host Galaxy ◽  
Excitation Mechanism ◽  
Shock Excitation ◽  
Excitation Mechanisms ◽  
Extended Emission

The excitation mechanism of the extended emission-line regions (EELRs) in Seyfert galaxies is commonly thought to be nuclear photoionization. However, some Seyfert galaxies have EELRs with disturbed kinematics, outflows, and morphology which is indicative of interaction between radio plasma and the ISM of the host galaxy. In these cases shock excitation must also be considered (BickneU 1993).To investigate the importance of shocks and photoionization, we have taken two approaches: mapping the spatial dependence of the line ratios, and using UV line ratios which are sensitive discriminants between shocks and photoionization.

scholarly journals Dust Distribution in IRAS Seyfert Galaxies

1994 ◽  
Vol 159 ◽  
pp. 355-355
Author(s):  
M. G. Pastoriza ◽  
Charles Bonatto ◽  
Eduardo Bica ◽  
T. Storchi-Bergmann
Keyword(s):  
Emission Line ◽  
Power Law ◽  
Dust Emission ◽  
Seyfert Galaxies ◽  
Emission Model ◽  
Line Region ◽  
Population Type ◽  
The Galaxy ◽  
Dilution Effects ◽  
Dust Distribution

Observational evidences of dust in the nuclear region of AGNs are substantial (Rudy 1984, ApJ, 284, 33; Jones et al. 1984, PASP, 96, 692). The ionization cones observed in several Seyfert galaxies has been interpreted as shadowing effects by a dust obscuring torus which hides the broad emission line region (BLR) and the central source (Wilson 1992; Storchi-Bergmann, Mulchaey and Wilson 1992, ApJ 395, L73). A large sample of optical and far-IR data for IRAS Seyfert galaxies has been analysed together with dust emission models (Bonatto and Pastoriza 1993), where it has been concluded that the same dust emission model can be applied to both Seyfert types. In order to further study the effects of dust in the spectra of active galactic nuclei, we have obtained spectrophotometry of 21 IRAS Seyfert galaxies in the range 3500–7200 Å and analyse them in conjuction with their IRAS fluxes. The stellar population type is derived from comparisons with normal galaxy templates using dilution effects in the K CaII line as discriminator. For 55% of the sample the population is of late type. For the rest, blue continua due to recent star formation and/or power-law may amount up to 30% at 4000Å. We conclude that the bulge stellar populations of IRAS Seyfert galaxies are similar to those of normal spirals, except that they are more reddened by E(B-V)i ∼ 0.20. Population-subtracted emission line ratios indicate on average stronger reddening for the narrow-line region (E(B-V)l ∼ 0.8. From photoionization models a power-law index for the ionizing continuum α=1.5, and a metallicity larger than solar are obtained. The most luminous IRAS galaxy of the sample (IRAS555) is discuss in detail: in order to be compatible with the observed IRAS fluxes and the optical stellar continuum, the ionizing continuum must be reddened by AV > 10 magnitudes. Consequently a dust structure in this galaxy appears to be increasingly affecting stars and gas towards the galaxy center.

scholarly journals On the Effects of Dissipative Turbulence on the Narrow Emission‐Line Ratios in Seyfert Galaxies

2007 ◽  
Vol 668 (2) ◽  
pp. 730-737 ◽  
Author(s):  
S. B. Kraemer ◽  
M. C. Bottorff ◽  
D. M. Crenshaw
Keyword(s):  
Emission Line ◽  
Seyfert Galaxies ◽  
Dissipative Turbulence ◽  
Narrow Emission

An Emission-Line Imaging Survey of Early-Type Seyfert Galaxies. II. Implications for Unified Schemes

1996 ◽  
Vol 467 ◽  
pp. 197 ◽  
Author(s):  
John S. Mulchaey ◽  
Andrew S. Wilson ◽  
Zlatan Tsvetanov
Keyword(s):  
Emission Line ◽  
Seyfert Galaxies ◽  
Early Type ◽  
Line Imaging

scholarly journals The case of NGC 6302: the impact of shocks in the derivation of nitrogen abundances

2019 ◽  
Vol 489 (2) ◽  
pp. 2923-2929
Author(s):  
P J A Lago ◽  
R D D Costa ◽  
M Faúndez-Abans ◽  
W J Maciel
Keyword(s):  
Emission Line ◽  
Correction Factor ◽  
Planetary Nebulae ◽  
Type I ◽  
Excitation Mechanism ◽  
High Nitrogen ◽  
Filamentary Structure ◽  
Usual Assumption ◽  
Nitrogen Abundance ◽  
The Impact

ABSTRACT High nitrogen abundance is characteristic of Type I planetary nebulae, as well as their highly filamentary structure. In the present work, we test the hypothesis of shocks as a relevant excitation mechanism for a Type I nebula, NGC 6302, using recently released diagnostic diagrams to distinguish shocks from photoexcitation. The construction of the diagrams depends on emission-line ratios and kinematical information. NGC 6302 shows the relevance of shocks in peripheral regions and their importance to the whole nebula. Using shocks, we question the usual assumption of ionization correction factor calculation, justifying a warning regarding broadly used abundance derivation methods. From kinematical analysis, we derive a new distance for NGC 6302 of $805\pm 143\,$ pc.

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