Context. Detailed high-resolution studies of active galactic nuclei (AGN) with mid-infrared (MIR) interferometry have revealed parsec-sized dust emission that is elongated in the polar direction in ...four sources. Aims. Using a larger, coherently analyzed sample of AGN observed with MIR interferometry, we aim to identify elongated MIR emission in a statistical sample of sources. More specifically, we wish to determine if there is indeed a preferred direction of the elongation and whether this direction is consistent with a torus-like structure or with a polar emission. Methods. We investigated the significance of the detection of an elongated shape in the MIR emission by fitting elongated Gaussian models to the interferometric data at 12 μm. We paid special attention to (1) the uncertainties caused by an inhomogeneous (u,v) coverage; (2) the typical errors in the measurements; and (3) the spatial resolution achieved for each object. Results. From our sample of 23 sources, we are able to find elongated parsec-scale, MIR emission in five sources: three type 2s, one type 1i, and one type 1. Elongated emission in four of these sources has been published before; NGC 5506 is a new detection. The observed axis ratios are typically around 2 and the position angle of the 12 μm emission for all the elongated sources always seems to be closer to the polar axis of the system than to the equatorial axis. Two other objects, NGC 4507 and MCG-5-23-16, with reasonably well-mapped (u,v) coverage and good signal-to-noise ratios, appear to have a less elongated 12 μm emission. Conclusions. Our finding that sources showing elongated MIR emission are preferentially extended in polar direction sets strong constraints on torus models or implies that both the torus and NLR/outflow region have to be modeled together. In addition, models used for SED fitting will have to be revised to include emission from polar dust.
Context. 3C 273, the nearest bright quasar, comprises a strong nuclear core and a bright, one-sided jet extending ~23 arcsec to the SW. The source has been the subject of imaging campaigns in all ...wavebands. Extensive observations of this source have been made with the Very Large Array and other telescopes as part of a campaign to understand the jet emission mechanisms. Partial results from the VLA radio campaign have been published, but to date, the complete set of VLA imaging results has not been made available. Aims. We have utilized the VLA to determine the radio structure of 3C 273 in Stokes I, Q, and U, over the widest possible frequency and resolution range. Methods. The VLA observed the source in all four of its configurations, and with all eight of its frequency bands, spanning 73.8 MHz to 43 GHz. The data were taken in a pseudo-spectral line mode to minimize the VLA’s correlator errors, and were fully calibrated with subsequent self-calibration techniques to maximise image fidelity. Results. Images in Stokes parameters I, Q, and U, spanning a resolution range from 6 arcsec to 88 milliarcsec are presented. Spectral index images, showing the evolution of the jet component are shown. Polarimetry demonstrates the direction of the magnetic fields responsible for the emission, and rotation measure maps show the RM to be very small with no discernible trend along or across the jet. This paper presents a small subset of these images to demonstrate the major characteristics of the source emission. A library of 294 images has been made available at the CDS.
Aims. The aim of this paper is to understand the relation in active galactic nuclei (AGNs) between the small obscuring torus and dusty structures at larger scales (5−10 pc). Methods. The dusty ...structures in AGNs are best observed in the mid-infrared. To achieve the necessary spatial resolution (20−100 millarcsec) we use ESO’s Mid-Infrared Interferometer (MIDI) with the 1.8 m Auxiliary Telescopes. We use the chromatic phases in the data to improve the spatial fidelity of the analysis. Results. 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 three-component best fit with estimates of sizes, temperatures, and positions of the components. A large, warm, offcenter component is required at a distance approximately 90 mas to the northwest at a position angle (PA) of ~−18°. Conclusions. The dust at 5−10 pc in the polar region contributes four times more to the mid-infrared flux at 12 μm 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).
A diversity of dusty AGN tori Burtscher, L; Meisenheimer, K; Tristram, K R W ...
Astronomy and astrophysics (Berlin),
10/2013, Letnik:
558
Journal Article
Recenzirano
The AGN-heated dust distribution is increasingly recognized not only as the absorber required in unifying models, but as a tracer for the reservoir that feeds the nuclear super-massive black hole. ...Yet, even its most basic structural properties are unknown for all but a few archetypical objects. In order to understand how the properties of AGN tori are related to feeding and obscuration, we need to resolve the matter distribution on parsec scales. Since most AGNs are unresolved in the mid-IR, even with the largest telescopes, we utilize the MID-infrared interferometric Instrument (MIDI) at the Very Large Telescope Interferometer (VLTI) that is sensitive to structures as small as a few milli-arcseconds. Variations in the relative contribution of extended dust in the narrow line region or heated by star formation vs. compact AGN-heated dust and non-thermal emission also have to be taken into account.
We present spectral energy distributions (SEDs) of 69 QSOs at z > 5, covering a rest frame wavelength range of 0.1 mu m to ~80 mu m, and centered on new Spitzer and Herschel observations. The ...detection rate of the QSOs with Spitzer is very high (97% at lambda sub(rest) lap 4 mu m), but drops toward the Herschel bands with 30% detected in PACS (rest frame mid-infrared) and 15% additionally in the SPIRE (rest frame far-infrared; FIR). We perform multi-component SED fits for Herschel-detected objects and confirm that to match the observed SEDs, a clumpy torus model needs to be complemented by a hot (~1300 K) component and, in cases with prominent FIR emission, also by a cold (~50 K) component. In the FIR-detected cases the luminosity of the cold component is of the order of 10 super(13) L sub(middot in circle) which is likely heated by star formation. From the SED fits we also determine that the active galactic nucleus (AGN) dust-to-accretion disk luminosity ratio declines with UV/optical luminosity. Emission from hot (~1300 K) dust is common in our sample, showing that nuclear dust is ubiquitous in luminous QSOs out to redshift 6. However, about 15% of the objects appear under-luminous in the near infrared compared to their optical emission and seem to be deficient in (but not devoid of) hot dust. Within our full sample, the QSOs detected with Herschel are found at the high luminosity end in L sub(UV/opt) and L sub(NIR) and show low equivalent widths (EWs) in H alpha and in Ly alpha . In the distribution of H alpha EWs, as determined from the Spitzer photometry, the high-redshift QSOs show little difference to low-redshift AGN.
Context. Tori of Active Galactic Nuclei (AGN) are made up of a mixture of hot and cold gas, as well as dust. In order to protect the dust grains from destruction by the surrounding hot gas as well as ...by the energetic (UV/optical) radiation from the accretion disk, the dust is often assumed to be distributed in clouds. Aims. A new three-dimensional model of AGN dust tori is extensively investigated. The torus is modelled as a wedge-shaped disk within which dusty clouds are randomly distributed throughout the volume, by taking the dust density distribution of the corresponding continuous model into account. We especially concentrate on the differences between clumpy and continuous models in terms of the temperature distributions, the surface brightness distributions and interferometric visibilities, as well as spectral energy distributions. Methods. Radiative transfer calculations with the help of the three-dimensional Monte Carlo radiative transfer code MC3D are used in order to simulate spectral energy distributions as well as surface brightness distributions at various wavelengths. In a second step, interferometric visibilities for various inclination as well as position angles and baselines are calculated, which can be used to directly compare our models to interferometric observations with the MIDI instrument. Results. We find that the radial temperature distributions of clumpy models possess significantly enhanced scatter compared to the continuous cases. Even at large distances, clouds can be heated directly by the central accretion disk. The existence of the silicate 10 μm-feature in absorption or in emission depends sensitively on the distribution, the size and optical depth of clouds in the innermost part of the dust distribution. With this explanation, failure and success of previous modelling efforts of clumpy tori can be understood. The main reason for this outcome are shadowing effects of clouds within the central region. We underline this result with the help of several parameter variations. After adapting the parameters of our clumpy standard model to the circumstances of the Seyfert 2 Circinus galaxy, it can qualitatively explain recent mid-infrared interferometric observations performed with MIDI, as well as high resolution spectral data.
Abstract
We present the Mid-infrared stellar Diameters and Fluxes compilation Catalogue (MDFC) dedicated to long-baseline interferometry at mid-infrared wavelengths (3–13 $\mu$m). It gathers data for ...half a million stars, i.e. nearly all the stars of the Hipparcos-Tycho catalogue whose spectral type is reported in the SIMBAD data base. We cross-match 26 data bases to provide basic information, binarity elements, angular diameter, magnitude and flux in the near and mid-infrared, as well as flags that allow us to identify the potential calibrators. The catalogue covers the entire sky with 465 857 stars, mainly dwarfs and giants from B to M spectral types closer than 18 kpc. The smallest reported values reach 0.16 $\mu$Jy in L and 0.1 $\mu$Jy in N for the flux, and 2 microarcsec for the angular diameter. We build four lists of calibrator candidates for the L and Nbands suitable with the Very Large Telescope Interferometer (VLTI) sub- and main arrays using the MATISSE instrument. We identify 1621 candidates for L and 44 candidates for N with the Auxiliary Telescopes (ATs), 375 candidates for both bands with the ATs, and 259 candidates for both bands with the Unit Telescopes (UTs). Predominantly cool giants, these sources are small and bright enough to belong to the primary lists of calibrator candidates. In the near future, we plan to measure their angular diameter with 1 per cent accuracy.
In this paper, we describe the first data release of the Visible and Infrared Survey Telescope for Astronomy (VISTA) Deep Extragalactic Observations (VIDEO) survey. VIDEO is a ∼12 deg2 survey in the ...near-infrared Z, Y, J, H and K
s bands, specifically designed to enable the evolution of galaxies and large structures to be traced as a function of both epoch and environment from the present day out to z = 4, and active galactic nuclei (AGNs) and the most massive galaxies up to and into the epoch of reionization. With its depth and area, VIDEO will be able to fully explore the period in the Universe where AGN and starburst activity were at their peak and the first galaxy clusters were beginning to virialize. VIDEO therefore offers a unique data set with which to investigate the interplay between AGN, starbursts and environment, and the role of feedback at a time when it was potentially most crucial.
We provide data over the VIDEO-XMM3 tile, which also covers the Canada-France-Hawaii Telescope Legacy Survey Deep-1 field (CFHTLS-D1). The released VIDEO data reach a 5σ AB-magnitude depth of Z = 25.7, Y = 24.5, J = 24.4, H = 24.1 and K
s = 23.8 in 2 arcsec diameter apertures (the full depth of Y = 24.6 will be reached within the full integration time in future releases). The data are compared to previous surveys over this field and we find good astrometric agreement with the Two Micron All Sky Survey, and source counts in agreement with the recently released UltraVISTA survey data. The addition of the VIDEO data to the CFHTLS-D1 optical data increases the accuracy of photometric redshifts and significantly reduces the fraction of catastrophic outliers over the redshift range 0 < z < 1 from 5.8 to 3.1 per cent in the absence of an i-band luminosity prior. However, we expect that the main improvement in photometric redshifts will come in the redshift range 1 < z < 4 due to the sensitivity to the Balmer and 4000 Å breaks provided by the near-infrared VISTA filters. All images and catalogues presented in this paper are publicly available through ESO's phase 3 archive and the VISTA Science Archive.
Spectral energy distributions (SEDs) of the central few tens of parsec region of some of the nearest, most well-studied, active galactic nuclei (AGN) are presented. These genuine AGN-core SEDs, ...mostly from Seyfert galaxies, are characterized by two main features: an infrared (IR) bump with the maximum in the 2–10 μm range and an increasing X-ray spectrum with frequency in the 1 to ∼200 keV region. These dominant features are common to Seyfert type 1 and 2 objects alike. In detail, type 1 AGN are clearly distinguished from type 2 by their high spatial resolution SEDs: type 2 AGN exhibit a sharp drop shortwards of 2 μm, with the optical to UV region being fully absorbed; type 1s instead show a gentle 2 μm drop ensued by a secondary, partially absorbed optical to UV emission bump. On the assumption that the bulk of optical to UV photons generated in these AGN is reprocessed by dust and re-emitted in the IR in an isotropic manner, the IR bump luminosity represents ≳70 per cent of the total energy output in these objects, and the second energetically important contribution is the high energies above 20 keV. Galaxies selected by their warm IR colours, i.e. presenting a relatively flat flux distribution in the 12–60 μm range, have often being classified as AGN. The results from these high spatial resolution SEDs question this criterion as a general rule. It is found that the intrinsic shape of the infrared SED of an AGN and inferred bolometric luminosity largely depart from those derived from large aperture data. AGN luminosities can be overestimated by up to two orders of magnitude if relying on IR satellite data. We find these differences to be critical for AGN luminosities below or about 1044 erg s−1. Above this limit, AGN tend to dominate the light of their host galaxy regardless of the integration aperture size used. Although the number of objects presented in this work is small, we tentatively mark this luminosity as a threshold to identify galaxy-light-dominated versus AGN-dominated objects.
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