The narrow-line region of intermediate Seyfert galaxies

Cohen, R. D.

doi:10.1086/161386

Cited by 91 publications

(109 citation statements)

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“…Historically, optical measurements of the NLRs in Seyfert 2 galaxies have noted significantly more reddening due to dust compared with Seyfert 1 galaxies (Cohen 1983;Gaskell 1984;Tsvetanov & Yancoulova 1989). These studies, however, found substantial amounts of reddening in the NLRs in Seyfert 1 galaxies as well, in contrast to our results.…”

Section: Narrow-line Ratios and Reddeninggmentioning

confidence: 99%

Probing the Dust Obscuration in Seyfert Galaxies using Infrared Spectroscopy. II. Implication for the Unification of Seyfert Galaxies

Rhee¹,

Larkin²

2005

ApJ

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We report near-IR spectroscopic observations of 11 Seyfert galaxies (six Seyfert 1s, one Seyfert 1.9, and four Seyfert 2s) and additional galaxies (four LINERs, two H ii, and one type 2 transition) for comparison, obtained using the Gemini twin-channel near-IR camera on the Shane 3 m telescope at Lick Observatory. With the unique design of the Gemini camera, full J and K spectra were taken simultaneously through the same slit. This produced accurate line ratios of hydrogen recombination lines over a large wavelength baseline. For the Seyfert 1s ( 1.5), the line ratios of Pa /Br are not only comparable in both broad-and narrow-line regions but also consistent with case B recombination, indicating little or no reddening in both narrow-and broad-line regions. Seyfert 2 (>1.5) galaxies, however, show substantial reddening toward the narrow-line regions. We compare optical reddening data from the literature and find significant support for the dichotomy between Seyfert 1s and Seyfert 2s, at least in lowluminosity objects. Two different scenarios are explored to explain the observed difference in reddening: a difference in reddening due to an extended dusty torus under active galactic nucleus unification, and a difference due to a different grain size distribution between the two Seyfert types. We also discuss a similar potential difference found in the strength of the 9.7 m silicate line, along with a possible correlation between the narrow-line reddening and the strength of the silicate absorption line. We also analyzed CO band head absorption features longward of 2.3 m to look for nonstellar contamination and evidence of recent star formation activity. The CO band head in Seyfert 1s shows heavy contamination from nonstellar radiation, which is correlated with an H À K nuclear color excess. We confirm that the CO spectroscopic indices in both Seyfert types do not show evidence of recent star formation. Taking the nonstellar contamination into account, there is little evidence from the CO index for a difference in star formation rates in the nuclei of Seyfert 1s and Seyfert 2s in our low-luminosity sample.

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Section: Narrow-line Ratios and Reddeninggmentioning

confidence: 99%

Probing the Dust Obscuration in Seyfert Galaxies using Infrared Spectroscopy. II. Implication for the Unification of Seyfert Galaxies

Rhee¹,

Larkin²

2005

ApJ

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“…For the BLSy1 model, we assumed an ionization parameter (number of ionizing photons per nucleon at the illuminated face of the zone) of U = 0.001, which yields a predicted [O III]/Hβ ratio of ≈ 10, typical for the NLR of Seyfert 1s (Cohen 1983). For the BLSy1 SED model and the average X-ray luminosity of the sample, 1.4 x 10 43 erg s −1 , the luminosity in ionizing photons is 1.7 x 10 54 photons s −1 , which places the gas at ∼ 200 pc from the central source.…”

Section: Luminosity Comparisonmentioning

confidence: 99%

On the Relationship between the Optical Emission‐Line and X‐Ray Luminosities in Seyfert 1 Galaxies

Kraemer

George

Crenshaw

et al. 2004

ApJ

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We have explored the relationship between the [O III] λ5007 and the 2-10 keV luminosities for a sample of Broad-and Narrow-Line Seyfert 1 galaxies (BLSy1 and NLSy1, respectively). We find that both types of Seyferts span the same range in luminosity and possess similar [O III]/X-ray ratios. The NLSy1s are more luminous than BLSy1s, when normalized to their central black hole masses, which is attributed to higher mass accretion rates. However, we find no evidence for elevated [O III]/X-ray ratios in NLSy1s, which would have been expected if they had excess EUV continuum emission compared to BLSy1s. Also, other studies suggest that the gas in narrow-line regions (NLR) of NLSy1s and NLSy1s span a similar range in ionization, contrary to what is expected if those of the former are exposed to a stronger flux of EUV radiation. The simplest interpretation is that, like BLSy1s, a large EUV bump is not present in NLSy1s. However, we show that the [OIII]/X-ray ratio can be lowered as a result of absorption of the ionizing continuum by gas close to the central source, although there is no evidence that intrinsic line-of-sight absorption is more common among NLSy1s, as would be expected if there were a larger amount of circumnuclear gas. Other possible explanations include: 1) anisotropic emission of the ionizing radiation, 2) higher gas densities in the NLR of NLSy1s, resulting in lower average

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“…As it is beyond the scope of this paper and the signal-to-noise ratio of many of the spectra to attempt a detailed deblending, I assume that the NLR contributes Hb with 1/10 the Ñux of [O III] j5007, and I subtract that from the Hb proÐle before modeling. The assumption is based on the results obtained from narrow-line emission from Seyfert 2 and intermediate Seyfert galaxies (e.g., Koski 1978 ;Cohen 1983).…”

Section: Rosat Datamentioning

confidence: 99%

A Comprehensive Spectral and Variability Study of Narrow‐Line Seyfert 1 Galaxies Observed by ASCA . II. Spectral Analysis and Correlations

Leighly

1999

ASTROPHYS J SUPPL S

315

197

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I present a comprehensive and uniform analysis of 25 ASCA observations from 23 narrow-line Seyfert 1 galaxies (NLS1s). The spectral analysis and correlations are presented in this paper ; the reduction and time series analysis are presented in the companion paper. A maximum likelihood analysis conÐrms that the hard X-ray photon index is signiÐcantly steeper at more than 90% conÐdence in this sample of NLS1s compared with a random sample of Seyfert galaxies with broad optical lines. Soft excess emission was detected in 17 of the 19 objects that had no signiÐcant absorption, a result that demonstrates that soft excesses appear considerably more frequently in NLS1s than in Seyfert 1 galaxies with broad optical lines. The strength of the soft excess, parameterized using a Ñux ratio obtained from the blackbody plus power-law model, has a wide range of values in these objects (a factor of 50). The photon index was found to be correlated with the Hb FWHM, despite the small range of the latter parameter ; however, neither parameter is correlated with the strength of the soft excess or ROSAT slope. Therefore, assuming that an excess of soft photons causes the steep photon index and narrow Hb FWHM, that excess may lie primarily in the unobservable EUV. The strength of the soft excess is correlated with the variability parameters, so that objects with strong soft excesses show higher amplitude variability ; this potentially important result is not easily explained. While a range of 2 orders of magnitude in luminosity is represented, the temperature of the soft excess is approximately consistent throughout the sample, in contrast with expectations of simple accretion disk models. The presence of ionized absorption was sought using a two-edge model. It was found that this component appears to be typically less common in NLS1s and some evidence was found that the typical ionization state is lower compared with broad-line Seyfert galaxies. This fact, plus evidence for a correlation between the presence of the warm absorber and signiÐcant optical polarization, may imply that the inner warm absorber is missing or is too highly ionized to be detected, and only the outer, dusty, less ionized warm absorber is present in many cases. The iron line equivalent width appears to be similar among narrow and broad-line Seyfert galaxies. This could mean that reprocessing occurs with similar geometry in both classes of objects ; however, the detection of ionized iron lines in a few objects, implying possibly altered Ñuorescence yields, and poor statistics, makes this conclusion tentative. Constraints on physical processes and models based on extreme values of orientation and accretion rate for NLS1s are examined in light of the observational results.

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The narrow-line region of intermediate Seyfert galaxies

Cited by 91 publications

References 0 publications

Probing the Dust Obscuration in Seyfert Galaxies using Infrared Spectroscopy. II. Implication for the Unification of Seyfert Galaxies

Probing the Dust Obscuration in Seyfert Galaxies using Infrared Spectroscopy. II. Implication for the Unification of Seyfert Galaxies

On the Relationship between the Optical Emission‐Line and X‐Ray Luminosities in Seyfert 1 Galaxies

A Comprehensive Spectral and Variability Study of Narrow‐Line Seyfert 1 Galaxies Observed by ASCA . II. Spectral Analysis and Correlations

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