214 research outputs found
Spoken content retrieval: A survey of techniques and technologies
Speech media, that is, digital audio and video containing spoken content, has blossomed in recent years. Large collections are accruing on the Internet as well as in private and enterprise settings. This growth has motivated extensive research on techniques and technologies that facilitate reliable indexing and retrieval. Spoken content retrieval (SCR) requires the combination of audio and speech processing technologies with methods from information retrieval (IR). SCR research initially investigated planned speech structured in document-like units, but has subsequently shifted focus to more informal spoken content produced spontaneously, outside of the studio and in conversational settings. This survey provides an overview of the field of SCR encompassing component technologies, the relationship of SCR to text IR and automatic speech recognition and user interaction issues. It is aimed at researchers with backgrounds in speech technology or IR who are seeking deeper insight on how these fields are integrated to support research and development, thus addressing the core challenges of SCR
Nuclear X-ray properties of the peculiar radio-loud hidden AGN 4C+29.30
We present results from a study of a nuclear emission of a nearby radio
galaxy, 4C+29.30, over a broad 0.5-200 keV X-ray band. This study used new
XMM-Newton (~17 ksec) and Chandra (~300 ksec) data, and archival Swift/BAT data
from the 58-month catalog. The hard (>2 keV) X-ray spectrum of 4C+29.30 can be
decomposed into an intrinsic hard power-law (Gamma ~ 1.56) modified by a cold
absorber with an intrinsic column density N_{H,z} ~ 5x10^{23} cm^{-2}, and its
reflection (|Omega/2pi| ~ 0.3) from a neutral matter including a narrow iron
Kalpha emission line at the rest frame energy ~6.4 keV. The reflected component
is less absorbed than the intrinsic one with an upper limit on the absorbing
column of N^{refl}_{H,z} < 2.5x10^{22} cm^{-2}. The X-ray spectrum varied
between the XMM-Newton and Chandra observations. We show that a scenario
invoking variations of the normalization of the power-law is favored over a
model with variable intrinsic column density. X-rays in the 0.5-2 keV band are
dominated by diffuse emission modeled with a thermal bremsstrahlung component
with temperature ~0.7 keV, and contain only a marginal contribution from the
scattered power-law component. We hypothesize that 4C+29.30 belongs to a class
of `hidden' AGN containing a geometrically thick torus. However, unlike the
majority of them, 4C+29.30 is radio-loud. Correlations between the scattering
fraction and Eddington luminosity ratio, and the one between black hole mass
and stellar velocity dispersion, imply that 4C+29.30 hosts a black hole with
~10^8 M_{Sun} mass.Comment: 13 pages, 5 figures, ApJ in pres
The Origin of the Silicate Emission Features in the Seyfert 2 Galaxy, NGC 2110
The unified model of active galactic nuclei (AGN) predicts silicate emission
features at 10 and 18 microns in type 1 AGN, and such features have now been
observed in objects ranging from distant QSOs to nearby LINERs. More
surprising, however, is the detection of silicate emission in a few type 2 AGN.
By combining Gemini and Spitzer mid-infrared imaging and spectroscopy of NGC
2110, the closest known Seyfert 2 galaxy with silicate emission features, we
can constrain the location of the silicate emitting region to within 32 pc of
the nucleus. This is the strongest constraint yet on the size of the silicate
emitting region in a Seyfert galaxy of any type. While this result is
consistent with a narrow line region origin for the emission, comparison with
clumpy torus models demonstrates that emission from an edge-on torus can also
explain the silicate emission features and 2-20 micron spectral energy
distribution of this object. In many of the best-fitting models the torus has
only a small number of clouds along the line of sight, and does not extend far
above the equatorial plane. Extended silicate-emitting regions may well be
present in AGN, but this work establishes that emission from the torus itself
is also a viable option for the origin of silicate emission features in active
galaxies of both type 1 and type 2.Comment: ApJL, accepte
The origin of the infrared emission in radio galaxies. III. Analysis of 3CRR objects
We present Spitzer photometric data for a complete sample of 19 low redshift
(z<0.1) 3CRR radio galaxies as part of our efforts to understand the origin of
the prodigious mid- to far-infrared (MFIR) emission from radio-loud AGN. Our
results show a correlation between AGN power (indicated by [OIII] 5007 emission
line luminosity) and 24 micron luminosity. This result is consistent with the
24 micron thermal emission originating from warm dust heated directly by AGN
illumination. Applying the same correlation test for 70 micron luminosity
against [OIII] luminosity we find this relation to suffer from increased
scatter compared to that of 24 micron. In line with our results for the
higher-radio-frequency-selected 2Jy sample, we are able to show that much of
this increased scatter is due to heating by starbursts which boost the
far-infrared emission at 70 micron in a minority of objects (17-35%). Overall
this study supports previous work indicating AGN illumination as the dominant
heating mechanism for MFIR emitting dust in the majority of low to intermediate
redshift radio galaxies (0.03<z<0.7), with the advantage of strong statistical
evidence. However, we find evidence that the low redshift broad-line objects
(z<0.1) are distinct in terms of their positions on the MFIR vs. [OIII]
correlations.Comment: 31 pages, 3 figures, accepted for publication to Ap
Isotropic Mid-Infrared Emission from the Central 100 pc of Active Galaxies
Dust reprocesses the intrinsic radiation of active galactic nuclei (AGNs) to
emerge at longer wavelengths. The observed mid-infrared (MIR) luminosity
depends fundamentally on the luminosity of the central engine, but in detail it
also depends on the geometric distribution of the surrounding dust. To quantify
this relationship, we observe nearby normal AGNs in the MIR to achieve spatial
resolution better than 100 pc, and we use absorption-corrected X-ray luminosity
as a proxy for the intrinsic AGN emission. We find no significant difference
between optically classified Seyfert 1 and 2 galaxies. Spectroscopic
differences, both at optical and IR wavelengths, indicate that the immediate
surroundings of AGNs is not spherically symmetric, as in standard unified AGN
models. A quantitative analysis of clumpy torus radiative transfer models shows
that a clumpy local environment can account for this dependence on viewing
geometry while producing MIR continuum emission that remains nearly isotropic,
as we observe, although the material is not optically thin at these
wavelengths. We find some luminosity dependence on the X-ray/MIR correlation in
the smallest scale measurements, which may indicate enhanced dust emission
associated with star formation, even on these sub-100 pc scales.Comment: 10 pages, 5 figures; accepted for publication in Ap
Detectability of low energy X-ray spectral components in type 1 AGN
In this paper we examine the percentage of type 1 AGN which require the
inclusion of a soft excess component and/or significant cold absorption in the
modelling of their X-ray spectra obtained by XMM-Newton. We do this by
simulating spectra which mimic typical spectral shapes in order to find the
maximum detectability expected at different count levels. We then apply a
correction to the observed percentages found for the Scott et al. (2011) sample
of 761 sources. We estimate the true percentage of AGN with a soft excess
component to be 75+/-23%, suggesting that soft excesses are ubiquitous in the
X-ray spectra of type 1 AGN. By carrying out joint fits on groups of low count
spectra in narrow z bins in which additional spectral components were not
originally detected, we show that the soft excess feature is recovered with a
mean temperature kT and blackbody to power-law normalisation ratio consistent
with those of components detected in individual high count spectra. Cold
absorption with nH values broadly consistent with those reported in individual
spectra are also recovered. We suggest such intrinsic cold absorption is found
in a minimum of ~5% of type 1 AGN and may be present in up to ~10%.Comment: 10 pages, 6 figures, 4 tables. Accepted for publication in MNRA
Testing the Unification Model for AGN in the Infrared: are the obscuring tori of Type 1 and 2 Seyferts different?
We present new mid-infrared (MIR) imaging data for three Type-1 Seyfert
galaxies obtained with T-ReCS on the Gemini-South Telescope at subarcsecond
resolution. Our aim is to enlarge the sample studied in a previous work to
compare the properties of Type-1 and Type-2 Seyfert tori using clumpy torus
models and a Bayesian approach to fit the infrared nuclear spectral energy
distributions (SEDs). Thus, the sample considered here comprises 7 Type-1, 11
Type-2, and 3 intermediate-type Seyferts. The unresolved IR emission of the
Seyfert 1 galaxies can be reproduced by a combination of dust heated by the
central engine and direct AGN emission, while for the Seyfert 2 nuclei only
dust emission is considered. These dusty tori have physical sizes smaller than
6 pc radius, as derived from our fits. Unification schemes of AGN account for a
variety of observational differences in terms of viewing geometry. However, we
find evidence that strong unification may not hold, and that the immediate
dusty surroundings of Type-1 and Type-2 Seyfert nuclei are intrinsically
different. The Type-2 tori studied here are broader, have more clumps, and
these clumps have lower optical depths than those of Type-1 tori. The larger
the covering factor of the torus, the smaller the probability of having direct
view of the AGN, and vice-versa. In our sample, Seyfert 2 tori have larger
covering factors and smaller escape probabilities than those of Seyfert 1. All
the previous differences are significant according to the Kullback-Leibler
divergence. Thus, on the basis of the results presented here, the
classification of a Seyfert galaxy as a Type-1 or Type-2 depends more on the
intrinsic properties of the torus rather than on its mere inclination towards
us, in contradiction with the simplest unification model.Comment: 21 pages, 14 figures, Appendix including supplementary figures.
Accepted by Ap
BayesCLUMPY: Bayesian Inference with Clumpy Dusty Torus Models
Our aim is to present a fast and general Bayesian inference framework based
on the synergy between machine learning techniques and standard sampling
methods and apply it to infer the physical properties of clumpy dusty torus
using infrared photometric high spatial resolution observations of active
galactic nuclei. We make use of the Metropolis-Hastings Markov Chain Monte
Carlo algorithm for sampling the posterior distribution function. Such
distribution results from combining all a-priori knowledge about the parameters
of the model and the information introduced by the observations. The main
difficulty resides in the fact that the model used to explain the observations
is computationally demanding and the sampling is very time consuming. For this
reason, we apply a set of artificial neural networks that are used to
approximate and interpolate a database of models. As a consequence, models not
present in the original database can be computed ensuring continuity. We focus
on the application of this solution scheme to the recently developed public
database of clumpy dusty torus models. The machine learning scheme used in this
paper allows us to generate any model from the database using only a factor
10^-4 of the original size of the database and a factor 10^-3 in computing
time. The posterior distribution obtained for each model parameter allows us to
investigate how the observations constrain the parameters and which ones remain
partially or completely undetermined, providing statistically relevant
confidence intervals. As an example, the application to the nuclear region of
Centaurus A shows that the optical depth of the clouds, the total number of
clouds and the radial extent of the cloud distribution zone are well
constrained using only 6 filters.Comment: 12 pages, 7 figures, accepted for publication in Ap
Infrared Spectral Energy Distributions of Seyfert Galaxies: Spitzer Space Telescope Observations of the 12 micron Sample of Active Galaxies
The mid-far-infrared spectral energy distributions (SEDs) of 83 active
galaxies, mostly Seyfert galaxies, selected from the extended 12 micron sample
are presented. The data were collected using all three instruments, IRAC, IRS,
and MIPS, aboard the Spitzer Space Telescope. The IRS data were obtained in
spectral mapping mode, and the photometric data from IRAC and IRS were
extracted from matched, 20 arcsec diameter circular apertures. The MIPS data
were obtained in SED mode, providing very low resolution spectroscopy (R ~ 20)
between ~ 55 and 90 microns in a larger, 20 by 30 arcsec synthetic aperture. We
further present the data from a spectral decomposition of the SEDs, including
equivalent widths and fluxes of key emission lines; silicate 10 and 18 micron
emission and absorption strengths; IRAC magnitudes; and mid-far infrared
spectral indices. Finally, we examine the SEDs averaged within optical
classifications of activity. We find that the infrared SEDs of Seyfert 1s and
Seyfert 2s with hidden broad line regions (HBLR, as revealed by
spectropolarimetry or other technique) are qualitatively similar, except that
Seyfert 1s show silicate emission and HBLR Seyfert 2s show silicate absorption.
The infrared SEDs of other classes with the 12 micron sample, including Seyfert
1.8-1.9, non-HBLR Seyfert 2 (not yet shown to hide a type 1 nucleus), LINER and
HII galaxies, appear to be dominated by star-formation, as evidenced by blue
IRAC colors, strong PAH emission, and strong far-infrared continuum emission,
measured relative to mid-infrared continuum emission.Comment: 78 pages, 13 figure
An original interferometric study of NGC 1068 with VISIR BURST mode images
We present 12.8 microns images of the core of NGC 1068 obtained with the
BURST mode of the VLT/VISIR. We trace structures under the diffraction limit of
one UT and we investigate the link between dust in the vicinity of the central
engine of NGC 1068, recently resolved by interferometry with MIDI, and more
extended structures. This step is mandatory for a multi-scale understanding of
the sources of mid-infrared emission in AGNs. A speckle processing of VISIR
BURST mode images was performed to extract very low spatial-frequency
visibilities, first considering the full field of VISIR BURST mode images and
then limiting it to the mask used for the acquisition of MIDI data. Extracted
visibilities are reproduced with a multi-component model. We identify two major
sources of emission: one compact < 85 mas, associated with the dusty torus, and
an elliptical one, (< 140) mas x 1187 mas at P.A.=-4 degrees from N to E. This
is consistent with previous deconvolution processes. The combination with MIDI
data reveals the close environment of the dusty torus to contribute to about 83
percent of the MIR flux seen by MIDI. This strong contribution has to be
considered in modeling long baseline interferometric data. It must be related
to the NS elongated component which is thought to originate from individually
unresolved dusty clouds and is located inside the ionization cone. Low
temperatures of the dusty torus are not challenged, emphasizing the scenarios
of clumpy torus.Comment: 10 pages, 7 figures, accepted for publication in A&
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