30,620 research outputs found
Reflection in Seyfert Galaxies and the Unified Model of AGN
We present a deep study of the average hard X-ray spectra of Seyfert
galaxies. We analyzed all public INTEGRAL IBIS/ISGRI data available on all the
165 Seyfert galaxies detected at z<0.2. Our final sample consists of 44 Seyfert
1's, 29 Seyfert 1.5's, 78 Seyfert 2's, and 14 Narrow Line Seyfert 1's. We
derived the average hard X-ray spectrum of each subsample in the 17-250keV
energy range. All classes of Seyfert galaxies show on average the same nuclear
continuum, as foreseen by the zeroth order unified model, with a cut-off energy
of Ec>200keV, and a photon index of Gamma ~1.8. Compton-thin Seyfert 2's show a
reflection component stronger than Seyfert 1's and Seyfert 1.5's. Most of this
reflection is due to mildly obscured (10^23 cm^-2 < NH < 10^24 cm^-2) Seyfert
2's, which have a significantly stronger reflection component
(R=2.2^{+4.5}_{-1.1}) than Seyfert 1's (R<=0.4), Seyfert 1.5's (R<= 0.4) and
lightly obscured (NH < 10^23 cm^-2) Seyfert 2's (R<=0.5). This cannot be
explained easily by the unified model. The absorber/reflector in mildly
obscured Seyfert 2's might cover a large fraction of the X-ray source, and have
clumps of Compton-thick material. The large reflection found in the spectrum of
mildly obscured Seyfert 2's reduces the amount of Compton-thick objects needed
to explain the peak of the cosmic X-ray background. Our results are consistent
with the fraction of Compton-thick sources being ~10%. The spectra of Seyfert
2's with and without polarized broad lines do not show significant differences,
the only difference between the two samples being the higher hard X-ray and
bolometric luminosity of Seyfert 2's with polarized broad lines. The average
hard X-ray spectrum of Narrow line Seyfert 1's is steeper than those of Seyfert
1's and Seyfert 1.5's, probably due to a lower energy of the cutoff.Comment: 19 pages, accepted for publication in Astronomy and Astrophysics,
final versio
On black hole masses, radio-loudness and bulge luminosities of Seyfert galaxies
We estimated black hole masses for 9 Seyfert 1 and 13 Seyfert 2 galaxies in
the Palomar and CfA bright Seyfert samples using the tight correlation between
black hole mass and bulge velocity dispersion. Combining other 13 Seyfert 1s
and 2 Seyfert 2s in these samples but with black hole masses measured recently
by reverberation mapping and stellar/gas dynamics, we studied the correlations
of black hole masses with radio loudness and bulge luminosities for a sample of
37 Seyfert galaxies. We found that if radio-loudness is measured using the
optical and radio luminosities of the nuclear components, the black hole masses
of radio-loud Seyfert 1s tend to increase with the radio-loudness. The black
hole masses of all Seyfert galaxies increase with the radio power, but Seyfert
galaxies have larger radio powers than nearby galaxies with the same black hole
masses. In addition, the correlation between black hole masses and bulge V-band
luminosities for Seyfert galaxies is consistent with that found for quasars and
normal galaxies. The combined sample of 37 Seyfert galaxies, 15 quasars and 30
normal galaxies suggests a possible universal nonlinear relation between black
hole and bulge masses, , which is
slightly steeper than that found recently by Laor (2001) for a smaller sample.
This nonlinear relation is supported by a larger sample including 65 Seyfert
galaxies. The different M(BH)/M(bulge) ratio for galaxies with different bulge
luminosities or different black hole masses may be explained by this relation.
These results are consistent with some theoretical implications and are
important for understanding the nature of radio emissions and the formation and
evolution of supermassive black holes and galaxies.Comment: 10 pages, A&A accepte
A Hidden Broad-Line Region in the Weak Seyfert 2 Galaxy NGC 788
We have detected a broad H alpha emission line in the polarized flux spectrum
of the Seyfert 2 galaxy NGC 788, indicating that it contains an obscured
Seyfert 1 nucleus. While such features have been observed in ~15 other Seyfert
2s, this example is unusual because it has a higher fraction of galaxy
starlight in its spectrum, a lower average measured polarization, and a
significantly lower radio luminosity than other hidden Seyfert 1s discovered to
date. This demonstrates that polarized broad-line regions can be detected in
relatively weak classical Seyfert 2s, and illustrates why well-defined,
reasonably complete spectropolarimetric surveys at H alpha are necessary in
order to assess whether or not all Seyfert 2s are obscured Seyfert 1s.Comment: 10 pages using (AASTEX) aaspp4.sty and 4 postscript figures.
Publications of the Astronomical Society of the Pacific, Research Notes, in
pres
Spitzer/IRS 5-35 um Low-Resolution Spectroscopy of the 12 um Seyfert Sample
We present low-resolution 5.5-35 um spectra for 103 galaxies from the 12 um
Seyfert sample, a complete unbiased 12 um flux limited sample of local Seyfert
galaxies selected from the IRAS Faint Source Catalog, obtained with the
Infrared Spectrograph (IRS) on-board Spitzer Space Telescope. For 70 of the
sources observed in the IRS mapping mode, uniformly extracted nuclear spectra
are presented for the first time. We performed an analysis of the continuum
emission, the strength of the Polycyclic Aromatic Hydrocarbon (PAH) and
astronomical silicate features of the sources. We find that on average, the
15-30 um slope of the continuum is alpha_{15-30}=-0.85+-0.61 for Seyfert 1s and
-1.53+-0.84 for Seyfert 2s, and there is substantial scatter in each type.
Moreover, nearly 32% of Seyfert 1s, and 9% of Seyfert 2s, display a peak in the
mid-infrared spectrum at 20 um, which is attributed to an additional hot dust
component. The PAH equivalent width decreases with increasing dust temperature,
asindicated by the global infrared color of the host galaxies. However, no
statistical difference in PAH equivalent width is detected between the two
Seyfert types, 1 and 2, of the same bolometric luminosity. The silicate
features at 9.7 and 18um in Seyfert 1 galaxies are rather weak, while Seyfert
2s are more likely to display strong silicate absorption. Those Seyfert 2s with
the highest silicate absorption also have high infrared luminosity and high
absorption (hydrogen column density N_H>10^23 cm^-2 as measured from the
X-rays. Finally, we propose a new method to estimate the AGN contribution to
the integrated 12 um galaxy emission, by subtracting the "star formation"
component in the Seyfert galaxies, making use of the tight correlation between
PAH 11.2 um luminosity and 12 um luminosity for star forming galaxies.Comment: accepted for publication in Ap
Spitzer/IRS Observations of Seyfert 1.8s and 1.9s: A Comparison with Seyfert 1s and Seyfert 2s
We present Spitzer Space Telescope mid-infrared spectra of 12 Seyfert 1.8 and
1.9 galaxies over the 5-38 um region. We compare the spectral characteristics
of this sample to those of 58 Seyfert 1 and Seyfert 2 galaxies from the Spitzer
archives. An analysis of the spectral shapes, the silicate 10 um feature and
the emission line fluxes have enabled us to characterize the mid-IR properties
of Seyfert 1.8/1.9s. We find that the equivalent widths of the 10 um silicate
feature are generally weak in all Seyfert galaxies, as previously reported by
several studies. The few Seyfert galaxies in this sample that show deep 10 um
silicate absorption features are highly inclined and/or merging galaxies. It is
likely that these absorption features originate primarily in the dusty
interstellar medium of the host galaxy rather than in a dusty torus on parsec
scales close to the central engine. We find that the equivalent width of the
polycyclic aromatic hydrocarbon (PAH) band at 6.2 um correlates strongly with
the 20-30 um spectral index. Either of these quantities are good indicators of
the amount of starburst contribution to the mid-IR spectra. The spectra of
Seyfert 1.8 and 1.9s are dominated by these starburst features, similar to most
Seyfert 2s. They show strong PAH bands and a strong red continuum toward 30 um.
The strengths of the high-ionization forbidden narrow emission lines [O IV]
25.89 um, [Ne III] 15.56 um and [Ne V] 14.32 um relative to [Ne II] 12.81 um
are weaker in Seyfert 1.8/1.9s and Seyfert 2s as compared to Seyfert 1s. The
weakness of high-ionization lines in Seyfert 1.8-1.9s is suggestive of
intrinsically weak active galactic nuclei (AGN) continua, and/or stronger star
formation activity leading to enhanced [Ne II]. We discuss the implications of
these observational results in the context of the Unified Model of AGN.Comment: 36 pages, 4 tables, 6 figures, Accepted for publication in The
Astrophysical Journal, December 200
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