3,891 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
A frameshift mutation in NOD2 associated with susceptibility to Crohn's disease
Crohn's disease is a chronic inflammatory disorder of the gastrointestinal tract, which is thought to result from the effect of environmental factors in a genetically predisposed host. A gene location in the pericentromeric region of chromosome 16, IBD1, that contributes to susceptibility to Crohn's disease has been established through multiple linkage studies(1-6), but the specific gene(s) has not been identified. NOD2, a gene that encodes a protein with homology to plant disease resistance gene products is located in the peak region of linkage on chromosome 16 (ref. 7). Here we show, by using the transmission disequilibium test and case-control analysis, that a frameshift mutation caused by a cytosine insertion, 3020insC, which is expected to encode a truncated NOD2 protein, is associated with Crohn's disease. Wild-type NOD2 activates nuclear factor NF-kappaB, making it responsive to bacterial lipopolysaccharides; however, this induction was deficient in mutant NOD2. These results implicate NOD2 in susceptibility to Crohn's disease, and suggest a link between an innate immune response to bacterial components and development of disease.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/62856/1/411603a0.pd
Mrk 609: resolving the circum-nuclear structure with near-infrared integral field spectroscopy
We present first results of near infrared J and H+K ESO-SINFONI integral
field spectroscopy of the composite starburst/Seyfert 1.8 galaxy Mrk 609. The
data were taken during the science verification period of SINFONI. We aim to
investigate the morphology and excitation conditions within the central 2 kpc.
Additional Nobeyama 45 m CO(1-0) data are presented, which we used to estimate
the molecular gas mass. The source was selected from a sample of adaptive
optics suitable, SDSS/ROSAT based, X-ray bright AGN with redshifts of 0.03 < z
< 1. This sample allows for a detailed study of the NIR properties of the
nuclear and host environments with high spectral and spatial resolution. Our
NIR data reveal a complex emission-line morphology, possibly associated with a
nuclear bar seen in the reconstructed continuum images. The detections of
[SiVI] and a broad Pa alpha component are clear indicators for the presence of
an accreting super-massive black hole at the center of Mrk 609. In agreement
with previous observations we find that the circum-nuclear emission is not
significantly extincted. The analysis of the high angular resolution
rotational-vibrational molecular hydrogen and forbidden [FeII] emission reveals
a LINER character of the nucleus. The large H_2 gas mass deduced from the
CO(1-0) observation provides the fuel needed to feed the starburst and Seyfert
activity in Mrk 609. High angular resolution imaging spectroscopy provides an
ideal tool to resolve the nuclear and starburst contribution in active
galaxies. We show that Mrk 609 exhibits LINER features, that appear to be
hidden in larger aperture visible/NIR spectra.Comment: published by A&A, 19 pages, 16 figures, version with high resolution
figures is available via http://www.ph1.uni-koeln.de/~zuther/mrk609.pd
Demystifying the coronal line region of active galactic nuclei: spatially resolved spectroscopy with HST
We present an analysis of STIS/HST optical spectra of a sample of ten Seyfert
galaxies aimed at studying the structure and physical properties of the
coronal-line region (CLR). The high-spatial resolution provided by STIS allowed
us to resolve the CLR and obtain key information about the kinematics of the
coronal-line gas, measure directly its spatial scale, and study the mechanisms
that drive the high-ionisation lines. We find CLRs extending from just a few
parsecs (~10 pc) up to 230 pc in radius, consistent with the bulk of the
coronal lines (CLs) originating between the BLR and NLR, and extending into the
NLR in the case of [FeVII] and [NeV] lines. The CL profiles strongly vary with
the distance to the nucleus. We observed line splitting in the core of some of
the galaxies. Line peak shifts, both red- and blue-shifts, typically reached
500 km/s, and even higher velocities (1000 km/s) in some of the galaxies. In
general, CLs follow the same pattern of rotation curves as low-ionisation lines
like [OIII]. From a direct comparison between the radio and the CL emission we
find that neither the strength nor the kinematics of the CLs scale in any
obvious and strong way with the radio jets. Moreover, the similarity of the
flux distributions and kinematics of the CLs and low-ionisation lines, the low
temperatures derived for the gas, and the success of photoionisation models to
reproduce, within a factor of few, the observed line ratios, point towards
photoionisation as the main driving mechanism of CLs.Comment: Accepted for publication in MNRAS. 27 pages, 21 figures, 4 table
Is IRAS 01072+4954 a True-Seyfert 2? Hints from Near Infrared Integral Field Spectroscopy
In contrast to the predictions of the unified model, some X-ray unobscured
Seyfert 2 galaxies have been discovered in the last decade. One of them, the
starburst/Seyfert composite galaxy IRAS 01072+4954 (z=0.0236), has a typical
Type~1 X-ray emission, while its optical spectrum resembles an HII galaxy and
lacks the expected broad lines. We performed near-infrared integral-field
observations of this object with the aim to determine the nature of its nuclear
emission and to find indications for the existence or absence of a broad-line
region. Several reasons have been proposed to explain such peculiar emission.
We studied the validity of such hypotheses, including the possibility for it to
be True-Seyfert~2. We found little obscuration towards the nucleus A_V = 2.5
mag, and a nuclear star-formation rate Sigma_SFR < 11.6 Msun yr^{-1} kpc^{-2},
which is below the average in Seyferts. Unresolved hot-dust emission with T ~
1150 K seems to indicate the presence of a torus with its axis close to the
line of sight. We found that IRAS 01072+4954 hosts a low mass black hole with
an estimated mass of M_BH ~ 10^5 Msun and an upper limit of 2.5x10^6 Msun. Its
bolometric luminosity is L_bol ~ 2.5x10^{42} erg/s, which yields a high
accretion rate with an Eddington ratio ~ 0.2. If the relations found in more
massive systems also apply to this case, then IRAS 01072+4954 should show broad
emission lines with FWHM_{broad} ~(400-600) km/s. Indeed, some indications for
such narrow broad-line components are seen in our data, but the evidence is not
yet conclusive. This source thus seems not to be a True-Seyfert 2, but an
extreme case of a narrow line Seyfert 1, which, due to the faintness of the
active nucleus, does not have strong FeII emission in the optical.Comment: 16 pages, 11 figures. A&A Accepted versio
Accelerated amyloid deposition, neurofibrillary degeneration and neuronal loss in double mutant APP/tau transgenic mice
Even though the idea that amyloid beta peptide accumulation is the primary event in the pathogenesis of Alzheimer's disease has become the leading hypothesis, the causal link between aberrant amyloid precursor protein processing and tau alterations in this type of dementia remains controversial. We further investigated the role of beta-amyloid production/deposition in tau pathology and neuronal cell death in the mouse brain by crossing Tg2576 and VLW lines expressing human mutant amyloid precursor protein and human mutant tau, respectively. The resulting double transgenic mice showed enhanced amyloid deposition accompanied by neurofibrillary degeneration and overt neuronal loss in selectively vulnerable brain limbic areas. These findings challenge the idea that tau pathology in Alzheimer's disease is merely a downstream effect of amyloid production/deposition and suggest that reciprocal interactions between beta-amyloid and tau alterations may take place in vivo
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