444 research outputs found
The subarcsecond mid-infrared view of local active galactic nuclei: III. Polar dust emission
Recent mid-infrared (MIR) interferometric observations showed in few active
galactic nuclei (AGN) that the bulk of the infrared emission originates from
the polar region above the putative torus, where only little dust should be
present. Here, we investigate whether such strong polar dust emission is common
in AGN. Out of 149 Seyferts in the MIR atlas of local AGN (Asmus et al.), 21
show extended MIR emission on single dish images. In 18 objects, the extended
MIR emission aligns with the system axis position angle, established by [OIII],
radio, polarisation and maser based position angle measurements. The relative
amount of resolved MIR emission is at least 40 per cent and scales with the
[OIV] fluxes implying a strong connection between the extended continuum and
[OIV] emitters. These results together with the radio-quiet nature of the
Seyferts support the scenario that the bulk of MIR emission is emitted by dust
in the polar region and not by the torus, which would demand a new paradigm for
the infrared emission structure in AGN. The current low detection rate of polar
dust in the AGN of the MIR atlas is explained by the lack of sufficient high
quality MIR data and the requirement for the orientation, NLR strength and
distance of the AGN. The James-Webb Space Telescope will enable much deeper
nuclear MIR studies with comparable angular resolution, allowing us to resolve
the polar emission and surroundings in most of the nearby AGN.Comment: Accepted for publication in ApJ on Mar 08 (submitted Dec 22
Differential interferometry of QSO broad line regions I: improving the reverberation mapping model fits and black hole mass estimates
Reverberation mapping estimates the size and kinematics of broad line regions
(BLR) in Quasars and type I AGNs. It yields size-luminosity relation, to make
QSOs standard cosmological candles, and mass-luminosity relation to study the
evolution of black holes and galaxies. The accuracy of these relations is
limited by the unknown geometry of the BLR clouds distribution and velocities.
We analyze the independent BLR structure constraints given by super-resolving
differential interferometry. We developed a three-dimensional BLR model to
compute all differential interferometry and reverberation mapping signals. We
extrapolate realistic noises from our successful observations of the QSO 3C273
with AMBER on the VLTI. These signals and noises quantify the differential
interferometry capacity to discriminate and measure BLR parameters including
angular size, thickness, spatial distribution of clouds, local-to-global and
radial-to-rotation velocity ratios, and finally central black hole mass and BLR
distance. A Markov Chain Monte Carlo model-fit, of data simulated for various
VLTI instruments, gives mass accuracies between 0.06 and 0.13 dex, to be
compared to 0.44 dex for reverberation mapping mass-luminosity fits. We
evaluate the number of QSOs accessible to measures with current (AMBER),
upcoming (GRAVITY) and possible (OASIS with new generation fringe trackers)
VLTI instruments. With available technology, the VLTI could resolve more than
60 BLRs, with a luminosity range larger than four decades, sufficient for a
good calibration of RM mass-luminosity laws, from an analysis of the variation
of BLR parameters with luminosity.Comment: 19 pages, 14 figures, accepted by MNRAS on December 5, 201
Assessing the Prosody of Non-Native Speakers of English: Measures and Feature Sets
In this paper, we describe a new database with audio recordings of non-native (L2) speakers of English, and the perceptual evaluation experiment conducted with native English speakers for assessing the prosody of each recording. These annotations are then used to compute the gold standard using different methods, and a series of regression experiments is conducted to evaluate their impact on the performance of a regression model predicting the degree of Abstract naturalness of L2 speech. Further, we compare the relevance of different feature groups modelling prosody in general (without speech tempo), speech rate and pauses modelling speech tempo (fluency), voice quality, and a variety of spectral features. We also discuss the impact of various fusion strategies on performance.Overall, our results demonstrate that the prosody of non-native speakers of English as L2 can be reliably assessed using supra- segmental audio features; prosodic features seem to be the most important ones
A dust-parallax distance of 19 megaparsecs to the supermassive black hole in NGC 4151
The active galaxy NGC 4151 has a crucial role as one of only two active
galactic nuclei for which black hole mass measurements based on emission line
reverberation mapping can be calibrated against other dynamical methods.
Unfortunately, effective calibration requires an accurate distance to NGC 4151,
which is currently not available. Recently reported distances range from 4 to
29 megaparsecs (Mpc). Strong peculiar motions make a redshift-based distance
very uncertain, and the geometry of the galaxy and its nucleus prohibit
accurate measurements using other techniques. Here we report a dust-parallax
distance to NGC 4151 of Mpc. The measurement is
based on an adaptation of a geometric method proposed previously using the
emission line regions of active galaxies. Since this region is too small for
current imaging capabilities, we use instead the ratio of the
physical-to-angular sizes of the more extended hot dust emission as determined
from time-delays and infrared interferometry. This new distance leads to an
approximately 1.4-fold increase in the dynamical black hole mass, implying a
corresponding correction to emission line reverberation masses of black holes
if they are calibrated against the two objects with additional dynamical
masses.Comment: Authors' version of a letter published in Nature (27 November 2014);
8 pages, 5 figures, 1 tabl
The dusty heart of nearby active galaxies. I. High-spatial resolution mid-IR spectro-photometry of Seyfert galaxies
We present 8-13 micron imaging and spectroscopy of 9 type 1 and 10 type 2 AGN
obtained with the VLT/VISIR instrument at spatial resolution <100 pc. The
emission from the host galaxy sources is resolved out in most cases. The
silicate absorption features are moderately deep and emission features are
shallow. We compare the mid-IR luminosities to AGN luminosity tracers and found
that the mid-IR radiation is emitted quite isotropically. In two cases, IC5063
and MCG-3-34-64, we find evidence for extended dust emission in the narrow-line
region. We confirm the correlation between observed silicate feature strength
and Hydrogen column density recently found in Spitzer data. In a further step,
our 3D clumpy torus model has been used to interpret the data. We show that the
strength of the silicate feature and the mid-IR spectral index can be used to
get reasonable constraints on the dust distribution in the torus. The mid-IR
spectral index, alpha, is almost exclusively determined by the radial dust
distribution power-law index, a, and the silicate feature depth is mostly
depending on the average number of clouds, N0, along an equatorial
line-of-sight and the torus inclination. A comparison of model predictions to
our type 1 and type 2 AGN reveals typical average parameters a=-1.0+/-0.5 and
N0=5-8, which means that the radial dust distribution is rather shallow. As a
proof-of-concept of this method, we compared the model parameters derived from
alpha and the silicate feature to more detailed studies of IR SEDs and
interferometry and found that the constraints on a and N0 are consistent.
Finally, we might have found evidence that the radial structure of the torus
changes from low to high AGN luminosities towards steeper dust distributions,
and we discuss implications for the IR size-luminosity relation. (abridged)Comment: 22 pages, 13 figues, 6 tables; Accepted for publication in A&A; Note
that this is the second submitted paper from the series, but we changed paper
order. This one will be referred to as paper I, the previously submitted
arXiv:0909.4539 will become paper I
Mapping the radial structure of AGN tori
We present mid-IR interferometric observations of 6 type 1 AGNs at multiple
baseline lengths of 27--130m, reaching high angular resolutions up to
lambda/B~0.02 arcseconds. For two of the targets, we have simultaneous near-IR
interferometric measurements as well. The multiple baseline data directly probe
the radial distribution of the material on sub-pc scales. Within our sample,
which is small but spans over ~2.5 orders of magnitudes in the UV/optical
luminosity L of the central engine, the radial distribution clearly and
systematically changes with luminosity. First, we show that the brightness
distribution at a given mid-IR wavelength seems to be rather well described by
a power law, which makes a simple Gaussian or ring size estimation quite
inadequate. Here we instead use a half-light radius R_1/2 as a representative
size. We then find that the higher luminosity objects become more compact in
normalized half-light radii R_1/2 /R_in in the mid-IR, where R_in is the dust
sublimation radius empirically given by the L^1/2 fit of the near-IR
reverberation radii. This means that, contrary to previous studies, the
physical mid-IR emission size (e.g. in pc) is not proportional to L^1/2, but
increases with L much more slowly, or in fact, nearly constant at 13 micron.
Combining the size information with the total flux specta, we infer that the
radial surface density distribution of the heated dust grains changes from a
steep ~r^-1 structure in high luminosity objects to a shallower ~r^0 structure
in those of lower luminosity. The inward dust temperature distribution does not
seem to smoothly reach the sublimation temperature -- on the innermost scale of
~R_in, a relatively low temperature core seems to co-exist with a slightly
distinct brightness concentration emitting roughly at the sublimation
temperature.Comment: accepted for publication in A&
The dusty torus in the Circinus galaxy: a dense disk and the torus funnel
(Abridged) With infrared interferometry it is possible to resolve the nuclear
dust distributions that are commonly associated with the dusty torus in active
galactic nuclei (AGN). The Circinus galaxy hosts the closest Seyfert 2 nucleus
and previous interferometric observations have shown that its nuclear dust
emission is well resolved.
To better constrain the dust morphology in this active nucleus, extensive new
observations were carried out with MIDI at the Very Large Telescope
Interferometer.
The emission is distributed in two distinct components: a disk-like emission
component with a size of ~ 0.2 1.1 pc and an extended component with a
size of ~ 0.8 1.9 pc. The disk-like component is elongated along PA ~
46{\deg} and oriented perpendicular to the ionisation cone and outflow. The
extended component is elongated along PA ~ 107{\deg}, roughly perpendicular to
the disk component and thus in polar direction. It is interpreted as emission
from the inner funnel of an extended dust distribution and shows a strong
increase in the extinction towards the south-east. We find no evidence of an
increase in the temperature of the dust towards the centre. From this we infer
that most of the near-infrared emission probably comes from parsec scales as
well. We further argue that the disk component alone is not sufficient to
provide the necessary obscuration and collimation of the ionising radiation and
outflow. The material responsible for this must instead be located on scales of
~ 1 pc, surrounding the disk.
The clear separation of the dust emission into a disk-like emitter and a
polar elongated source will require an adaptation of our current understanding
of the dust emission in AGN. The lack of any evidence of an increase in the
dust temperature towards the centre poses a challenge for the picture of a
centrally heated dust distribution.Comment: 30 pages, 12 figures; A&A in pres
Modeling the optical/UV polarization while flying around the tilted outflows of NGC 1068
Recent modeling of multi-waveband spectroscopic and maser observations
suggests that the ionized outflows in the nuclear region of the archetypal
Seyfert-2 galaxy NGC 1068 are inclined with respect to the vertical axis of the
obscuring torus. Based on this suggestion, we build a complex reprocessing
model of NGC 1068 for the optical/UV band. We apply the radiative transfer code
STOKES to compute polarization spectra and images. The effects of electron and
dust scattering and the radiative coupling occurring in the inner regions of
the multi-component object are taken into account and evaluated at different
polar and azimuthal viewing angles. The observed type-1/type-2 polarization
dichotomy of active galactic nuclei is reproduced. At the assumed observer's
inclination toward NGC 1068, the polarization is dominated by scattering in the
polar outflows and therefore it indicates their tilting angle with respect to
the torus axis. While a detailed analysis of our model results is still in
progress, we briefly discuss how they relate to existing polarization
observations of NGC 1068.Comment: To appear in the proceedings of the meeting "The Central Kiloparsec
in Galactic Nuclei" held in Bad Honnef (Germany) from August 29th to
September 2nd 201
High-Spatial Resolution SED of NGC 1068 from Near-IR to Radio. Disentangling the thermal and non-thermal contributions
We investigate the ideas that a sizable fraction of the interferometrically
unresolved infrared emission of the nucleus of NGC 1068 might originate from
other processes than thermal dust emission from the torus. We examine the
contribution of free-free or synchrotron emissions to the central mid- and
near-IR parsec-scale emitting region of NGC 1068. Each mechanism is constrained
with parsec scale radio data available for NGC 1068 in the 10^9 - 10^11 Hz
regime, and compared to the highest-resolution interferometric data available
in the mid-infrared. It is shown that the unresolved emission in the
interferometric observation (<~1pc) is still dominatedd by dust emission and
not by contributions from synchrotron or free-free emission. As recent studies
suggest, the interferometric observations prefer a clumpy structure of the dust
distribution. Extrapolation of the radio free-free or synchrotron emission to
the IR indicates that their contribution is <20% even for the unresolved
fraction of the interferometric flux. The slope of the available radio data is
consistent with a power law exponent alpha = 0.29 +/- 0.07 which we interprete
in terms of either free-free emission or synchrotron radiation from
quasi-monochromatic electrons. We apply emission models for both mechanisms in
order to obtain physical parameters. (abridged)Comment: 8 pages, 3 figures; accepted by A&
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