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

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

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

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 $D_A = 19.0^{+2.4}_{-2.6}$ 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 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 $\times$ 1.1 pc and an extended component with a size of ~ 0.8 $\times$ 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

Identification of a new short-period comet near the sun

We present the identification of comet C/1999 R1 (SOHO) with comet C/2003 R5 (SOHO). Both apparitions were only observed with the Solar and Heliospheric Observatory (SOHO) at distances smaller than 0.1 AU from the sun with the LASCO coronagraphs onboard the spacecraft. Although SOHO comets usually have poor orbital coverage, the 1999 and 2003 arcs are sufficient to generate a link that seems to satisfy all observations. We also analyze comet C/2002 R5 (SOHO) which has similar orbital elements. A fragmentation scenario is proposed and discussed which would support the linkage of C/1999 R1 and C/2003 R5 and thus its short periodic nature.Comment: 5 pages, 1 figure; accepted for publication in A&

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&

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&

Exploring the inner region of Type 1 AGNs with the Keck interferometer

The exploration of extragalactic objects with long-baseline interferometers in the near-infrared has been very limited. Here we report successful observations with the Keck interferometer at K-band (2.2 um) for four Type 1 AGNs, namely NGC4151, Mrk231, NGC4051, and the QSO IRAS13349+2438 at z=0.108. For the latter three objects, these are the first long-baseline interferometric measurements in the infrared. We detect high visibilities (V^2 ~ 0.8-0.9) for all the four objects, including NGC4151 for which we confirm the high V^2 level measured by Swain et al.(2003). We marginally detect a decrease of V^2 with increasing baseline lengths for NGC4151, although over a very limited range, where the decrease and absolute V^2 are well fitted with a ring model of radius 0.45+/-0.04 mas (0.039+/-0.003 pc). Strikingly, this matches independent radius measurements from optical--infrared reverberations that are thought to be probing the dust sublimation radius. We also show that the effective radius of the other objects, obtained from the same ring model, is either roughly equal to or slightly larger than the reverberation radius as a function of AGN luminosity. This suggests that we are indeed partially resolving the dust sublimation region. The ratio of the effective ring radius to the reverberation radius might also give us an approximate probe for the radial structure of the inner accreting material in each object. This should be scrutinized with further observations.Comment: accepted for publication in A&A Letter