2,525 research outputs found
Obscuring and feeding supermassive black holes with evolving nuclear star clusters
Recently, high resolution observations with the help of the near-infrared
adaptive optics integral field spectrograph SINFONI at the VLT proved the
existence of massive and young nuclear star clusters in the centres of a sample
of Seyfert galaxies. With the help of high resolution hydrodynamical
simulations with the PLUTO-code, we follow the evolution of such clusters,
especially focusing on mass and energy feedback from young stars. This leads to
a filamentary inflow of gas on large scales (tens of parsec), whereas a
turbulent and very dense disc builds up on the parsec scale. Here, we
concentrate on the long-term evolution of the nuclear disc in NGC 1068 with the
help of an effective viscous disc model, using the mass input from the large
scale simulations and accounting for star formation in the disc. This two-stage
modelling enables us to connect the tens of parsec scale region (observable
with SINFONI) with the parsec scale environment (MIDI observations). At the
current age of the nuclear star cluster, our simulations predict disc sizes of
the order of 0.8 to 0.9 pc, gas masses of 1.0e6 Msun and mass transfer rates
through the inner boundary of 0.025 Msun/yr in good agreement with values
derived from observations.Comment: 6 pages, 3 figures, to appear in the proceedings of the IAU General
Assembly 2009, Rio de Janeiro, S267 Co-evolution of Central Black Holes and
Galaxie
Time-resolved infrared emission from radiation-driven central obscuring structures in Active Galactic Nuclei
The central engines of Seyfert galaxies are thought to be enshrouded by
geometrically thick gas and dust structures. In this article, we derive
observable properties for a self-consistent model of such toroidal gas and dust
distributions, where the geometrical thickness is achieved and maintained with
the help of X-ray heating and radiation pressure due to the central engine.
Spectral energy distributions (SEDs) and images are obtained with the help of
dust continuum radiative transfer calculations with RADMC-3D. For the first
time, we are able to present time-resolved SEDs and images for a physical model
of the central obscurer. Temporal changes are mostly visible at shorter
wavelengths, close to the combined peak of the dust opacity as well as the
central source spectrum and are caused by variations in the column densities of
the generated outflow. Due to the three-component morphology of the
hydrodynamical models -- a thin disc with high density filaments, a surrounding
fluffy component (the obscurer) and a low density outflow along the rotation
axis -- we find dramatic differences depending on wavelength: whereas the
mid-infrared images are dominated by the elongated appearance of the outflow
cone, the long wavelength emission is mainly given by the cold and dense disc
component. Overall, we find good agreement with observed characteristics,
especially for those models, which show clear outflow cones in combination with
a geometrically thick distribution of gas and dust, as well as a geometrically
thin, but high column density disc in the equatorial plane.Comment: 16 pages, 12 figures, accepted for publication in MNRA
Revealing the large nuclear dust structures in NGC 1068 with MIDI/VLTI
To understand the relation between the small "obscuring torus" and dusty
structures at larger scales (5-10 pc) in NGC 1068, we use ESO's Mid-Infrared
Interferometer (MIDI) with the 1.8 m Auxiliary Telescopes to achieve the
necessary spatial resolution (~ 20-100 millarcsec). We use the chromatic phases
in the data to improve the spatial fidelity of the analysis. We present
interferometric data for NGC 1068 obtained in 2007 and 2012. We find no
evidence of source variability. Many (u,v) points show non-zero chromatic
phases indicating significant asymmetries. Gaussian model fitting of the
correlated fluxes and chromatic phases provides a 3-component best fit with
estimates of sizes, temperatures and positions of the components. A large,
warm, off-center component is required at a distance approximately 90 mas to
the north-west at a PA ~ -18 deg. The dust at 5-10 pc in the polar region
contributes 4 times more to the mid-infrared flux at 12 um than the dust
located at the center. This dust may represent the inner wall of a dusty cone.
If similar regions are heated by the direct radiation from the nucleus, then
they will contribute substantially to the classification of many Seyfert
galaxies as Type 2. Such a region is also consistent in other Seyfert galaxies
(the Circinus galaxy, NGC 3783 and NGC 424).Comment: 21 pages, 10 figures; Accepted for publication on A&
Data analysis methods for the cosmic microwave background
41 pages, 21 figuresInternational audienceIn this review, we give an overview of some of the major aspects of data reduction and analysis for the cosmic microwave background (CMB). Since its prediction and discovery in the last century, the CMB radiation has proven itself to be one of our most valuable tools for precision cosmology. Recently, and especially when combined with complementary cosmological data, measurements of the CMB anisotropies have provided us with a wealth of quantitive information about the birth, evolution and structure of our Universe. We begin with a simple, general introduction to the physics of the CMB, including a basic overview of the experiments which record CMB data. The focus, however, will be the data analysis treatment of CMB data sets
Radiative transfer modelling of parsec-scale dusty warped discs
Warped discs have been found on (sub-)parsec scale in some nearby Seyfert
nuclei, identified by their maser emission. Using dust radiative transfer
simulations we explore their observational signatures in the infrared in order
to find out whether they can partly replace the molecular torus. Strong
variations of the brightness distributions are found, depending on the
orientation of the warp with respect to the line of sight. Whereas images at
short wavelengths typically show a disc-like and a point source component, the
warp itself only becomes visible at far-infrared wavelengths. A similar variety
is visible in the shapes of the spectral energy distributions. Especially for
close to edge-on views, the models show silicate feature strengths ranging from
deep absorption to strong emission for variations of the lines of sight towards
the warp. To test the applicability of our model, we use the case of the
Circinus galaxy, where infrared interferometry has revealed a highly elongated
emission component matching a warped maser disc in orientation and size. Our
model is for the first time able to present a physical explanation for the
observed dust morphology as coming from the AGN heated dust. As opposed to
available torus models, a warped disc morphology produces a variety of silicate
feature shapes for grazing lines of sight, close to an edge-on view. This could
be an attractive alternative to a claimed change of the dust composition for
the case of the nearby Seyfert 2 galaxy NGC 1068, which harbours a warped maser
disc as well.Comment: accepted by MNRA
Embedded AGN and star formation in the central 80 pc of IC 3639
[Abridged] Methods: We use interferometric observations in the -band with
VLTI/MIDI to resolve the mid-IR nucleus of IC 3639. The origin of the nuclear
infrared emission is determined from: 1) the comparison of the correlated
fluxes from VLTI/MIDI with the fluxes measured at subarcsec resolution
(VLT/VISIR, VLT/ISAAC); 2) diagnostics based on IR fine-structure line ratios,
the IR continuum emission, IR bands produced by polycyclic aromatic
hydrocarbons (PAH) and silicates; and 3) the high-angular resolution spectral
energy distribution. Results: The unresolved flux of IC 3639 is at , measured with three different baselines in
VLTI (UT1-UT2, UT3-UT4, and UT2-UT3; -), making this the
faintest measurement so far achieved with mid-IR interferometry. The correlated
flux is a factor of - times fainter than the VLT/VISIR total flux
measurement. The observations suggest that most of the mid-IR emission has its
origin on spatial scales between and (-). A composite scenario where the star formation component dominates
over the AGN is favoured by the diagnostics based on ratios of IR
fine-structure emission lines, the shape of the IR continuum, and the PAH and
silicate bands. Conclusions: A composite AGN-starburst scenario is able to
explain both the mid-IR brightness distribution and the IR spectral properties
observed in the nucleus of IC 3639. The nuclear starburst would dominate the
mid-IR emission and the ionisation of low-excitation lines (e.g. [NeII]) with a net contribution of . The AGN accounts for the
remaining of the mid-IR flux, ascribed to the unresolved component
in the MIDI observations, and the ionisation of high-excitation lines (e.g.
[NeV] and [OIV]).Comment: Accepted for publication in A&
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