14,445 research outputs found
Spectral Models for Low-luminosity Active Galactic Nuclei in LINERs: The Role of Advection-dominated Accretion and Jets
We perform an exploratory study of the physical properties of accretion flows
and jets in low-luminosity active galactic nuclei (LLAGNs) by modeling the
spectral energy distributions (SEDs) of 12 LLAGNs in low-ionization nuclear
emission-line regions (LINERs). These SEDs we constructed from high-resolution
radio, X-ray and optical/UV observations of the immediate vicinity of the black
hole. We adopt a coupled accretion-jet model comprising an inner
advection-dominated accretion flow (ADAF) and an outer standard thin disk. We
present best-fit models in which either the ADAF or the jet dominate the X-ray
emission. Six sources in our sample display an optical-UV excess with respect
to ADAF and jet models; this excess can be explained as emission from the
truncated disk with transition radii 30-225 Rs in four of them. In almost all
sources the optical emission can also be attributed to unresolved, old stellar
clusters with masses ~1E7-1E8 Msun. We find evidence for a correlation between
the accretion rate and jet power and an anti-correlation between the
radio-loudness and the accretion rate. We confirm previous findings that the
radio emission is severely underpredicted by ADAF models and explained by the
relativistic jet. We find evidence for a nonlinear relation between the X-ray
and bolometric luminosities and a slight IR excess in the average model SED
compared to that of quasars. We suggest that the hardness of the X-ray spectrum
can be used to identify the X-ray emission mechanism and discuss directions for
progress in understanding the origin of the X-rays.Comment: Accepted for publication in MNRAS. 27 pages, 22 figures. arXiv admin
note: substantial text overlap with arXiv:1112.464
A correlation between the highest energy cosmic rays and nearby active galactic nuclei detected by Fermi
We analyze the correlation of the positions of gamma-ray sources in the Fermi
Large Area Telescope First Source Catalog (1FGL) and the First LAT Active
Galactic Nuclei (AGN) Catalog (1LAC) with the arrival directions of
ultra-high-energy cosmic rays (UHECRs) observed with the Pierre Auger
Observatory, in order to investigate the origin of UHECRs. We find that
Galactic sources and blazars identified in the 1FGL are not significantly
correlated with UHECRs, while the 1LAC sources display a mild correlation (2.6
sigma level) on a ~2.4 degree angular scale. When selecting only the 1LAC AGNs
closer than 200 Mpc, we find a strong association (5.4 sigma) between their
positions and the directions of UHECRs on a ~17 degree angular scale; the
probability of the observed configuration being due to an isotropic flux of
cosmic rays is 5x10^{-8}. There is also a 5 sigma correlation with nearby 1LAC
sources on a 6.5 degree scale. We identify 7 "gamma-ray loud" AGNs which are
associated with UHECRs within ~17 degree and are likely candidates for the
production sites of UHECRs: Centaurus A, NGC 4945, ESO 323-G77, 4C+04.77, NGC
1218, RX J0008.0+1450 and NGC 253. We interpret these results as providing
additional support to the hypothesis of the origin of UHECRs in nearby
extragalactic objects. As the angular scales of the correlations are large, we
discuss the possibility that intervening magnetic fields might be considerably
deflecting the trajectories of the particles on their way to Earth.Comment: 23 pages, 7 figures, accepted for publication in Ap
2D stellar population and gas kinematics of the inner 1.5 kpc of the post-starburst quasar SDSS J0210-0903
Post-Starburst Quasars (PSQs) are hypothesized to represent a stage in the
evolution of massive galaxies in which the star formation has been recently
quenched due to the feedback of the nuclear activity. In this paper our goal is
to test this scenario with a resolved stellar population study of the PSQ
J0210-0903, as well as of its emitting gas kinematics and excitation. We have
used optical Integral Field Spectroscopy obtained with the Gemini GMOS
instrument at a velocity resolution of ~120 km/s and spatial resolution of ~0.5
kpc. We find that old stars dominate the luminosity (at 4700 \AA) in the inner
0.3 kpc (radius), while beyond this region (at ~0.8 kpc) the stellar population
is dominated by both intermediate age and young ionizing stars. The gas
emission-line ratios are typical of Seyfert nuclei in the inner 0.3 kpc, where
an outflow is observed. Beyond this region the line ratios are typical of
LINERs and may result from the combination of diluted radiation from the
nucleus and ionization from young stars. The gas kinematics show a combination
of rotation in the plane of the galaxy and outflows, observed with a maximum
blueshift of -670 km/s. We have estimated a mass outflow rate in ionized gas in
the range 0.3--1.1 M_sun/yr and a kinetic power for the outflow of dE/dt ~
1.4--5.0 x 10^40 erg/s ~0.03% - 0.1% x L_bol. This outflow rate is two orders
of magnitude higher than the nuclear accretion rate of ~8.7 x 10^-3 M_sun/yr,
thus being the result of mass loading of the nuclear outflow by circumnuclear
galactic gas. Our observations support an evolutionary scenario in which the
feeding of gas to the nuclear region has triggered a circumnuclear starburst
100's Myr ago, followed by the triggering of the nuclear activity, producing
the observed gas outflow which may have quenched further star formation in the
inner 0.3 kpc.Comment: 17 pages, 9 Figures, 2 Table
2D stellar population and gas kinematics of the inner kiloparsec of the post-starburst quasar SDSS J0330-0532
We have used optical Integral Field Spectroscopy in order to map the star
formation history of the inner kiloparsec of the Post-Starburst Quasar (PSQ)
J0330--0532 and to map its gas and stellar kinematics as well as the gas
excitation. PSQs are hypothesized to represent a stage in the evolution of
galaxies in which the star formation has been recently quenched due to the
feedback of the nuclear activity, as suggested by the presence of the
post-starburst population at the nucleus. We have found that the old stellar
population (age 2.5 Gyr) dominates the flux at 5100 \AA\ in the inner
0.26 kpc, while both the post-starburst (100 Myr age 2.5 Gyr) and
starburst (age 100 Myr) components dominate the flux in a circumnuclear
ring at 0.5 kpc from the nucleus. With our spatially resolved study we
do not have found any post-starburst stellar population in the inner 0.26\,kpc.
On the other hand, we do see the signature of AGN feedback in this region,
which does not reach the circumnuclear ring where the post-starburst population
is observed. We thus do not support the quenching scenario for the J0330-0532.
In addition, we have concluded that the strong signature of the post-starburst
population in larger aperture spectra (e.g. from Sloan Digital Sky Survey) is
partially due to the combination of the young and old age components. Based on
the M relationship and the stellar kinematics we
have estimated a mass for the supermassive black hole of 1.48 0.66
10 M.Comment: 16 pages, 11 figures. arXiv admin note: text overlap with
arXiv:1210.120
Gas rotation, shocks and outflow within the inner 3 kpc of the radio galaxy 3C 33
We present optical integral field spectroscopy obtained with the Gemini
Multi-Object Spectrograph of the inner kpc of the
narrow line radio galaxy 3C 33 at a spatial resolution of 0.58 kpc. The gas
emission shows three brightest structures: a strong knot of nuclear emission
and two other knots at kpc south-west and north-east of the
nucleus along the ionization axis. We detect two kinematic components in the
emission lines profiles, with a "broader component" (with velocity dispersion
km s) being dominant within a 1 kpc wide strip
("the nuclear strip") running from the south-east to the north-west,
perpendicular to the radio jet, and a narrower component ( km
s) dominating elsewhere. Centroid velocity maps reveal a rotation
pattern with velocity amplitudes reaching km s in the
region dominated by the narrow component, while residual blueshifts and
redshifts relative to rotation are observed in the nuclear strip, where we also
observe the highest values of the [N II]/H{\alpha}, [S II]/H{\alpha} and [O
I]/H{\alpha} line ratios, and an increase of the gas temperature (
K), velocity dispersion and electron density ( cm). We
interpret these residuals and increased line ratios as due to a lateral
expansion of the ambient gas in the nuclear strip due to shocks produced by the
passage of the radio jet. The effect of this expansion in the surrounding
medium is very small, as its estimated kinetic power represents only of the AGN bolometric luminosity. A possible signature of
inflow is revealed by an increase in the [O I]/H{\alpha} ratio values and
velocity dispersions in the shape of two spiral arms extending to 2.3 kpc
north-east and south-west from the nucleus.Comment: 16 pages, 14 figures, accepted by MNRA
Fibroblast growth factor receptor 4 single nucleotide polymorphism Gly388Arg in head and neck carcinomas
BACKGROUND Head and neck squamous cell carcinoma (HNSCC) is considered to be a progressive disease resulting from alterations in multiple genes regulating cell proliferation and differentiation like receptor tyrosine kinases (RTKs) and members of the fibroblast growth factor receptors (FGFR)-family. Single-nucleotide polymorphism (SNP) Arg388 of the FGFR4 is associated with a reduced overall survival in patients with cancers of various types. We speculate that FGFR4 expression and SNP is associated with worse survival in patients with HSNCC. AIM To investigate the potential clinical significance of FGFR4 Arg388 in the context of tumors arising in HNSCC, a comprehensive analysis of FGFR4 receptor expression and genotype in tumor tissues and correlated results with patients' clinical data in a large cohort of patients with HNSCC was conducted. METHODS Surgical specimens from 284 patients with HNSCC were retrieved from the Institute of Pathology at the Ludwig-Maximilian-University in Germany. Specimens were analyzed using immunohistochemistry and polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). The expression of FGFR4 was analyzed in 284 surgical specimens of HNSCC using immunohistochemstry. FGFR4 polymorphism was detected by PCR-RFLP. Patients' clinical data with a minimum follow-up of 5 syears were statistically evaluated with a special emphasis on survival analysis employing Kaplan-Meier estimator and Cox regression analysis. RESULTS Concerning the invasive tumor areas the intensity of the FGFR4 expression was evaluated in a four-grade system: no expression, low expression, intermediate and high expression. FGFR4 expression was scored as "high" (+++) in 74 (26%), "intermediate" (++) in 103 (36.3%), and "low" (+) in 107 (36.7%) cases. Analyzing the FGFR4 mutation it was found in 96 tumors (33.8%), 84 of them (29.6%) having a heterozygous and 12 (4.2%) homozygous mutated Arg388 allele. The overall frequency concerning the mutant alleles demonstrated 65% vs 34% mutated alleles in general. FGFR4 Arg388 was significantly associated with advanced tumor stage (P < 0.004), local metastasis (P < 0.0001) and reduced disease-free survival (P < 0.01). Furthermore, increased expression of FGFR4 correlated significantly with worse overall survival (P < 0.003). CONCLUSION In conclusion, the FGFR4 Arg388 genotype and protein expression of FGFR4 impacts tumor progression in patients with HNSCC and may present a useful target within a multimodal therapeutic intervention
New design of electrostatic mirror actuators for application in high-precision interferometry
We describe a new geometry for electrostatic actuators to be used in sensitive laser interferometers, suited for prototype and table top experiments related to gravitational wave detection with mirrors of 100 g or less. The arrangement consists of two plates at the sides of the mirror (test mass), and therefore does not reduce its clear aperture as a conventional electrostatic drive (ESD) would do. Using the sample case of the AEI-10 m prototype interferometer, we investigate the actuation range and the influence of the relative misalignment of the ESD plates with respect to the test mass. We find that in the case of the AEI-10 m prototype interferometer, this new kind of ESD could provide a range of 0.28 μm when operated at a voltage of 1 kV. In addition, the geometry presented is shown to provide a reduction factor of about 100 in the magnitude of the actuator motion coupling to the test mass displacement. We show that therefore in the specific case of the AEI-10 m interferometer, it is possible to mount the ESD actuators directly on the optical table without spoiling the seismic isolation performance of the triple stage suspension of the main test masses
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