1,569 research outputs found
Distribution of dust clouds around the central engine of NGC 1068
We studied the distribution of dust clouds around the central engine of NGC
1068 based on shifted-and-added 8.8 - 12.3 micron (MIR) multi-filter images and
3.0 - 3.9 micron (L-band) spectra obtained with the Subaru Telescope. In a
region of 100 pc (1.4") around the central peak, we successfully constructed
maps of color temperatures and emissivities of the MIR and L-band continua as
well as the 9.7 micron and 3.4 micron dust features with spatial resolutions of
26 pc (0.37") in the MIR and 22 pc (0.3") in the L-band. Our main results are:
1) color temperature of the MIR continuum scatters around the thermal
equilibrium temperature with the central engine as the heat source while that
of the L-band continuum is higher and independent upon distance from the
central engine; 2) the peak of the 9.7 micron silicate absorption feature is
shifted to a longer wavelength at some locations; 3) the ratio of the optical
depths of the dust features is different from the Galactic values and show
complicated spatial distribution; and 4) there is a pie shaped warm dust cloud
as an enhancement in the emissivity of the MIR continuum extending about 50 pc
to the north from the central engine. We speculate that material falls into the
central engine through this cloud.Comment: 26 pages, 9 figures. Accepted for publication on Ap
Dust Emission from Active Galactic Nuclei
Unified schemes of active galactic nuclei (AGN) require an obscuring dusty
torus around the central source, giving rise to Seyfert 1 line spectrum for
pole-on viewing and Seyfert 2 characteristics in edge-on sources. Although the
observed IR is in broad agreement with this scheme, the behavior of the 10
micron silicate feature and the width of the far-IR emission peak remained
serious problems in all previous modeling efforts. We show that these problems
find a natural explanation if the dust is contained in about 5-10 clouds along
radial rays through the torus. The spectral energy distributions (SED) of both
type 1 and type 2 sources are properly reproduced from different viewpoints of
the same object if the visual optical depth of each cloud is larger than about
60 and the clouds' mean free path increases roughly in proportion to radial
distance.Comment: 11 pages, submitted to ApJ Letter
An Advanced Colour Calibration Method for Fish Freshness Assessment: a Comparison Between Standard and Passive Refrigeration Modalities
Freshness represents a pivotal aspect in fish product for both security and quality. Its evaluation still represents the key factor driving the consumer' choices. Fish appearance is affected by many different factors that demand the contribution of different disciplines to be understood: from the physical and optical properties to the slaughtering and post-slaughtering conditions. An innovative preservation system is represented by the Passive Refrigeration PRS (TM) developed for the preservation and transport of perishable food products. Scientific methods for product freshness evaluation may be conveniently divided into two categories: sensorial and instrumental. In this study, an instrumental method of colour calibration and discrimination is proposed at pilot scale for automatic evaluation of gilthead seabream (Sparus aurata) freshness. We propose a non-destructive method based on the colorimetric imaging of the whole external body of seabreams to evaluate through multivariate partial least squares which approach the differences in the freshness preservation under four refrigeration modalities. The matrix of the independent variables is represented by RGB values for each pixel belonging to an extracted region of interest (129,633 values). The dependent variable is composed by two dummy variable corresponding to fresh (T-0) or non-fresh (T-2) individuals. T-1 individuals were used as external test. The results quantified significant colorimetric differences between fresh and non-fresh fish. All fish used to create the model (T-0 and T-2) were correctly classified as fresh or non-fresh, while external test individuals (T-1) were all classified as fresh. The proposed imaging method merges different image analysis techniques: (a) colorimetric calibration, (b) morphometric superimposition and (c) partial least square discriminant analysis modelling. This innovative and non-destructive approach allows the automatic assessment of fish freshness
The Transverse Proximity Effect: A Probe to the Environment, Anisotropy, and Megayear Variability of QSOs
The transverse proximity effect is the expected decrease in the strength of
the Lya forest absorption in a QSO spectrum when another QSO lying close to the
line of sight enhances the photoionization rate above that due to the average
cosmic ionizing background. We select three QSOs from the Early Data Release of
the Sloan Digital Sky Survey that have nearby foreground QSOs, with proper line
of sight tangential separations of 0.50, 0.82, and 1.10 h^{-1} Mpc. We estimate
that the ionizing flux from the foreground QSO should increase the
photoionization rate by a factor (94, 13, 13) in these three cases, which would
be clearly detectable in the first QSO and marginally so in the other two. We
do not detect the transverse proximity effect. Three possible explanations are
provided: an increase of the gas density in the vicinity of QSOs, time
variability, and anisotropy of the QSO emission. We find that the increase of
gas density near QSOs can be important if they are located in the most massive
halos present at high redshift, but is not enough to fully explain the absence
of the transverse proximity effect. Anisotropy requires an unrealistically
small opening angle of the QSO emission. Variability demands that the
luminosity of the QSO with the largest predicted effect was much lower 10^6
years ago, whereas the transverse proximity effect observed in the HeII Lya
absorption in QSO 0302-003 by Jakobsen et al. (2003) implies a lifetime longer
than 10^7 years. A combination of all three effects may better explain the lack
of Lya absorption reduction. A larger sample of QSO pairs may be used to
diagnose the environment, anisotropy and lifetime distribution of QSOs.Comment: 27 pages, 13 figures, accepted by Ap
VLTI/VINCI observations of the nucleus of NGC 1068 using the adaptive optics system MACAO
We present the first near-infrared K-band long-baseline interferometric
measurement of the prototype Seyfert 2 galaxy NGC 1068 with resolution lambda/B
\~ 10 mas obtained with the Very Large Telescope Interferometer (VLTI) and the
two 8.2m Unit Telescopes UT2 and UT3. The adaptive optics system MACAO was
employed to deliver wavefront-corrected beams to the K-band commissioning
instrument VINCI. A squared visibility amplitude of 16.3 +/- 4.3 % was measured
for NGC 1068 at a sky-projected baseline length of 45.8 m and azimuth angle
44.9 deg. This value corresponds to a FWHM of the K-band intensity distribution
of 5.0 +/- 0.5 mas (0.4 +/- 0.04 pc) at the distance of NGC 1068) if it
consists of a single Gaussian component. Taking into account K-band speckle
interferometry observations (Wittkowski et al. 1998; Weinberger et al. 1999;
Weigelt et al. 2004), we favor a multi-component model for the intensity
distribution where a part of the flux originates from scales clearly smaller
than about 5 mas (<0.4 pc), and another part of the flux from larger scales.
The K-band emission from the small (< 5 mas) scales might arise from
substructure of the dusty nuclear torus, or directly from the central accretion
flow viewed through only moderate extinction.Comment: Accepted for publication in Astronomy and Astrophysics Letter
Connecting Galaxy Evolution, Star Formation and the X-ray Background
As a result of deep hard X-ray observations by Chandra and XMM-Newton a
significant fraction of the cosmic X-ray background (CXRB) has been resolved
into individual sources. These objects are almost all active galactic nuclei
(AGN) and optical followup observations find that they are mostly obscured Type
2 AGN, have Seyfert-like X-ray luminosities (i.e., L_X ~ 10^{43-44} ergs
s^{-1}), and peak in redshift at z~0.7. Since this redshift is similar to the
peak in the cosmic star-formation rate, this paper proposes that the obscuring
material required for AGN unification is regulated by star-formation within the
host galaxy. We test this idea by computing CXRB synthesis models with a ratio
of Type 2/Type 1 AGN that is a function of both z and 2-10 keV X-ray
luminosity, L_X. The evolutionary models are constrained by parameterizing the
observed Type 1 AGN fractions from the recent work by Barger et al. The
parameterization which simultaneously best accounts for Barger's data, the CXRB
spectrum and the X-ray number counts has a local, low-L_X Type 2/Type 1 ratio
of 4, and predicts a Type 2 AGN fraction which evolves as (1+z)^{0.3}. Models
with no redshift evolution yielded much poorer fits to the Barger Type 1 AGN
fractions. This particular evolution predicts a Type 2/Type 1 ratio of 1-2 for
log L_X > 44, and thus the deep X-ray surveys are missing about half the
obscured AGN with these luminosities. These objects are likely to be Compton
thick. Overall, these calculations show that the current data strongly supports
a change to the AGN unification scenario where the obscuration is connected
with star formation in the host galaxy rather than a molecular torus alone. The
evolution of the obscuration implies a close relationship between star
formation and AGN fueling, most likely due to minor mergers or interactions.Comment: 36 pages, 8 figures, ApJ in press. Minor changes to match published
versio
Aromatic Features in AGN: Star-Forming Infrared Luminosity Function of AGN Host Galaxies
We describe observations of aromatic features at 7.7 and 11.3 um in AGN of
three types including PG, 2MASS and 3CR objects. The feature has been
demonstrated to originate predominantly from star formation. Based on the
aromatic-derived star forming luminosity, we find that the far-IR emission of
AGN can be dominated by either star formation or nuclear emission; the average
contribution from star formation is around 25% at 70 and 160 um. The
star-forming infrared luminosity functions of the three types of AGN are
flatter than that of field galaxies, implying nuclear activity and star
formation tend to be enhanced together. The star-forming luminosity function is
also a function of the strength of nuclear activity from normal galaxies to the
bright quasars, with luminosity functions becoming flatter for more intense
nuclear activity. Different types of AGN show different distributions in the
level of star formation activity, with 2MASS> PG> 3CR star formation rates.Comment: Accepted for publication in ApJ, 24 pages, 13 figure
Multivariate forecasting model to optimize management of grape downy mildew control
Aim of this study was to develop a forecasting model for Plasmopara viticola to achieve rational disease management and to reduce the use of copper treatments in organic farming. Starting from meteo-climatic, agronomic and phytopathological data a partial least squares discriminant analysis was developed. Three different strategies were compared: treatments according to the established organic agricultural practice (standard); treatments according to the predictive model and untreated control where no fungicides against downy mildew were applied. The modelling approach was divided into three phases: 1) model calibration; 2) field testing and 3) a posteriori model performance evaluation. The prediction was separately considered and modelled for: i) disease onset and ii) disease progress. The results for phase 1 show a percentage of correct classification equal to 91.8 % for the disease onset with 3 days elapsed between the prediction of first potential attack and disease onset and to 91.23 % for disease progress. In field testing phase the percentage of correct classification was equal to about 81 % for both the analysed years (2009 and 2010). In the phase 3 the percentages were quietly higher for the 2009. The number of fungicide applications on the partial least squares discriminant analysis model was almost half compared with standard schedule both in 2009 and 2010. Finally this approach showed the possibility to reduce fungicidal treatments and to avoid applying copper not essential for disease control representing a first step in the model validation
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