A. Asensio Ramos

TESTING THE UNIFICATION MODEL FOR ACTIVE GALACTIC NUCLEI 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 (CT=0.95� 0.02) and smaller escape probabilities (Pesc=0.05� 0.08 0.03 %) than those of Seyfert 1 (CT=0.5� 0.1; Pesc=18� 3 %). All the previous differences are significant according to the KullbackLeibler 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. Subject headings: galaxies: active – galaxies: nuclei – galaxies: Seyfert – infrared: galaxies

The Infrared Nuclear Emission of Seyfert Galaxies on Parsec Scales: Testing the Clumpy Torus Models

We present subarcsecond resolution mid-infrared (mid-IR) photometry in the wavelength range from 8 to 20 μm of 18 Seyfert galaxies, reporting high spatial resolution nuclear fluxes for the entire sample. We construct spectral energy distributions (SEDs) that the active galactic nucleus (AGN) dominates, relatively uncontaminated by starlight, adding near-IR measurements from the literature at similar angular resolution. We find that the IR SEDs of intermediate-type Seyferts are flatter and present higher 10 to 18 μm ratios than those of Seyfert 2 galaxies. We fit the individual SEDs with clumpy dusty torus models using the in-house-developed BayesClumpy tool. We find that the clumpy models reproduce the high spatial resolution measurements. Regardless of the Seyfert type, even with high spatial resolution data, near- to mid-IR SED fitting poorly constrains the radial extent of the torus. For the Seyfert 2 galaxies, we find that edge-on geometries are more probable than face-on views, with a number of clouds along equatorial rays of N 0 = 5-15. The 10 μm silicate feature is generally modeled in shallow absorption. For the intermediate-type Seyferts, N 0 and the inclination angle of the torus are lower than those of the Seyfert 2 nuclei, with the silicate feature appearing in weak emission or absent. The columns of material responsible for the X-ray absorption are larger than those inferred from the model fits for most of the galaxies, which is consistent with X-ray absorbing gas being located within the dust sublimation radius, whereas the mid-IR flux arises from an area farther from the accretion disk. The fits yield both the bolometric luminosity of the intrinsic AGN and the torus-integrated luminosity, from which we derive the reprocessing efficiency of the torus. In the models, the outer radial extent of the torus scales with the AGN luminosity, and we find the tori to be confined to scales less than 5 pc.

ADVANCED FORWARD MODELING AND INVERSION OF STOKES PROFILES RESULTING FROM THE JOINT ACTION OF THE HANLE AND ZEEMAN EFFECTS

A big challenge in solar and stellar physics in the coming years will be to decipher the magnetism of the solar outer atmosphere (chromosphere and corona) along with its dynamic coupling with the magnetic fields of the underlying photosphere. To this end, it is important to develop rigorous diagnostic tools for the physical interpretation of spectropolarimetric observations in suitably chosen spectral lines. Here we present a computer program for the synthesis and inversion of Stokes profiles caused by the joint action of atomic level polarization and the Hanle and Zeeman effects in some spectral lines of diagnostic interest, such as those of the He I 10830 A and 5876 A (or D3) multiplets. It is based on the quantum theory of spectral line polarization, which takes into account in a rigorous way all the relevant physical mechanisms and ingredients (optical pumping, atomic level polarization, level crossings and repulsions, Zeeman, Paschen-Back, and Hanle effects). The influence of radiative transfer on the emergent spectral line radiation is taken into account through a suitable slab model. The user can either calculate the emergent intensity and polarization for any given magnetic field vector or infer the dynamical and magnetic properties from the observed Stokes profiles via an efficient inversion algorithm based on global optimization methods. The reliability of the forward modeling and inversion code presented here is demonstrated through several applications, which range from the inference of the magnetic field vector in solar active regions to determining whether or not it is canopy-like in quiet chromospheric regions. This user-friendly diagnostic tool called HAZEL (from HAnle and ZEeman Light) is offered to the astrophysical community, with the hope that it will facilitate new advances in solar and stellar physics.

Triaxial stellar systems following the r1/n luminosity law: an analytical mass–density expression, gravitational torques and the bulge/disc interplay

We have investigated the structural and dynamical properties of triaxial stellar systems whose surface brightness profiles follow the r 1 / n luminosity law - extending the analysis by Ciotti, who explored the propertiesof spherical r 1 / n systems. A new analytical expression that accurately reproduces the spatial (i.e., deprojected) luminosity density profiles (error less than 0.1 per cent) is presented for detailed modelling of the Sersic family of luminosity profiles. We evaluate both the symmetric and the non-axisymmetric components of the gravitational potential and force, and compute the torques as a function of position. For a given triaxiality, stellar systems with smaller values of n have a greater non-axisymmetric gravitational field component. We also explore the strength of the non-axisymmetric forces produced by bulges with differing n and triaxiality on systems having a range of bulge-to-disc ratios. The increasing disc-to-bulge ratio with increasing galaxy type (decreasing n) is found to greatly reduce the amplitude of the non-axisymmetric terms, and therefore reduce the possibility that triaxial bulges in late-type systems may be the mechanism or perturbation for non-symmetric structures in the disc. Using seeing-convolved r 1 / n -bulge plus exponential-disc fits to the K-band data from a sample of 80 nearby disc galaxies, we probe the relations between galaxy type, Sersic index n and the bulge-to-disc luminosity ratio. These relations are shown to be primarily a consequence of the relation between n and the total bulge luminosity. In the K band, the trend of decreasing bulge-to-disc luminosity ratio along the spiral Hubble sequence is predominantly, though not entirely, a consequence of the change in the total bulge luminosity; the trend between the total disc luminosity and Hubble type is much weaker.

An Open Source, Massively Parallel Code for Non-LTE Synthesis and Inversion of Spectral Lines and Zeeman-induced Stokes Profiles

With the advent of a new generation of solar telescopes and instrumentation, interpreting chromospheric observations (in particular, spectropolarimetry) requires new, suitable diagnostic tools. This paper describes a new code, NICOLE, that has been designed for Stokes non-LTE radiative transfer, for synthesis and inversion of spectral lines and Zeeman-induced polarization profiles, spanning a wide range of atmospheric heights from the photosphere to the chromosphere. The code features a number of unique features and capabilities and has been built from scratch with a powerful parallelization scheme that makes it suitable for application on massive datasets using large supercomputers. The source code is written entirely in Fortran 90/2003 and complies strictly with the ANSI standards to ensure maximum compatibility and portability. It is being publicly released, with the idea of facilitating future branching by other groups to augment its capabilities.

Returning magnetic flux in sunspot penumbrae

Aims. We study the presence of reversed polarity magnetic flux in su nspot penumbra. Methods. We applied a new regularized method to deconvolve spectropolarimetric data observed with the spectropolarimeter SP onboard Hinode. The new regularization is based on a principal component decomposition of the Stokes profiles. The resul ting Stokes profiles were inverted to infer the magnetic field vect or using SIR. Results. We find, for the first time, reversed polarity fields at the bord er of many bright penumbral filaments in the whole penumbra.

PCA detection and denoising of Zeeman signatures in polarised stellar spectra

Aims. Our main objective is to develop a denoising strategy to increase the signal to noise ratio of individual spectral lines of stellar spectropolarimetric observations. Methods. We use a multivariate statistics technique called Principal Component Analysis. The cross-product matrix of the observations is diagonalized to obtain the eigenvectors in which the original observations can be developed. This basis is such that the first eigenvectors contain the greatest variance. Assuming that the noise is uncorrelated a denoising is possible by reconstructing the data with a truncated basis. We propose a method to identify the number of eigenvectors for an efficient noise filtering. Results. Numerical simulations are used to demonstrate that an important increase of the signal to noise ratio per spectral line is possible using PCA denoising techniques. It can be also applied for detection of magnetic fields in stellar atmospheres. We analyze the relation between PCA and commonly used techniques like line addition and least-squares deconvolution. Moreover, PCA is very robust and easy to compute.

The magnetic field configuration of a solar prominence inferred from spectropolarimetric observations in the He i 10 830 Å triplet

Context: The determination of the magnetic field vector in quiescent solar prominences is possible by interpreting the Hanle and Zeeman effects in spectral lines. However, observational measurements are scarce and lack high spatial resolution. Aims: To determine the magnetic field vector configuration along a quiescent solar prominence by interpreting spectropolarimetric measurements in the He I 1083.0 nm triplet obtained with the Tenerife Infrared Polarimeter installed at the German Vacuum Tower Telescope of the Observatorio del Teide. Methods. The He I 1083.0 nm triplet Stokes profiles are analyzed with an inversion code that takes into account the physics responsible of the polarization signals in this triplet. The results are put into a solar context with the help of extreme ultraviolet observations taken with the Solar Dynamic Observatory and the Solar Terrestrial Relations Observatory satellites. Results: For the most probable magnetic field vector configuration, the analysis depicts a mean field strength of 7 gauss. We do not find local variations in the field strength except that the field is, in average, lower in the prominence body than in the prominence feet, where the field strength reaches 25 gauss. The averaged magnetic field inclination with respect to the local vertical is 77 degrees. The acute angle of the magnetic field vector with the prominence main axis is 24 degrees for the sinistral chirality case and 58 degrees for the dextral chirality. These inferences are in rough agreement with previous results obtained from the analysis of data acquired with lower spatial resolutions.

Near-IR internetwork spectro-polarimetry at different heliocentric angles

Aims. The analysis of near infrared spectropolarimetric data at the internetwork in different regions on the solar surface could offer constraints that reject current modeling of these quiet areas. Methods. We present spectro-polarimetric observations of very quiet regions for different values of the heliocentric angle for the Fe i lines at 1.56 µm, from disc centre to positions close to the limb. The spatial resolution of the data is 0.7−1 �� . We analyse direct observable properties of the Stokes profiles as the amplitude of circular and linear polarisation, as well as the total degree of polarisation. The area and amplitude asymmetries are also studied. Results. We do not find any significant variation in the properties of the polarimetric signals with the heliocentric angle. This means that the magnetism of the solar internetwork remains the same regardless of the position on the solar disc. This observational fact discards the possibility of modeling the internetwork as a network-like scenario. The magnetic elements of internetwork areas seem to be isotropically distributed when observed at our spatial resolution.

Nonequilibrium CO Chemistry in the Solar Atmosphere

Investigating the reliability of the assumption of instantaneous chemical equilibrium (ICE) for calculating the CO number density in the solar atmosphere is of crucial importance for the resolution of the long-standing controversy over the existence of ‘cool clouds’ in the chromosphere, and for determining whether the cool gas owes its existence to CO radiative cooling or to a hydrodynamical process. Here we report the first results of such an investigation in which we have carried out time-dependent gas-phase chemistry calculations in radiation hydrodynamical simulations of solar chromospheric dynamics. We show that while the ICE approximation turns out to be suitable for modeling the observed infrared CO lines at the solar disk center, it may substantially overestimate the ‘heights of formation’ of strong CO lines synthesized close to the edge of the solar disk, especially concerning vigorous dynamic cases resulting from relatively strong photospheric disturbances. This happens because during the cool phases of the hydrodynamical simulations the CO number density in the outer atmospheric regions is smaller than what is stipulated by the ICE approximation, resulting in decreased CO opacity in the solar chromosphere. As a result, the cool CO-bearing gas which produces the observed molecular lines must be located at atmospheric heights not greater than 700 km, approximately. We conclude that taking into account the non-equilibrium chemistry improves the agreement with the available on-disk and off-limb observations, but that the hydrodynamical simulation model has to be even cooler than anticipated by the ICE approximation, and this has to be the case at the ‘new’ (i.e. deeper) formation regions of the rovibrational CO lines. Subject headings: astrochemistry—molecular processes—radiative transfer—Sun: chromosphere