Testing the Unification Model for AGN 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 and smaller escape probabilities than those of Seyfert 1. All the previous differences are significant according to the Kullback-Leibler 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.Comment: 21 pages, 14 figures, Appendix including supplementary figures. Accepted by Ap

Torus and AGN properties of nearby Seyfert galaxies: Results from fitting IR spectral energy distributions and spectroscopy

We used the CLUMPY torus models and a Bayesian approach to fit the infrared spectral energy distributions (SEDs) and ground-based high-angular resolution mid-infrared spectroscopy of 13 nearby Seyfert galaxies. This allowed us to put tight constraints on torus model parameters such as the viewing angle, the radial thickness of the torus Y, the angular size of the cloud distribution sigma_torus, and the average number of clouds along radial equatorial rays N_0. The viewing angle is not the only parameter controlling the classification of a galaxy into a type 1 or a type 2. In principle type 2s could be viewed at any viewing angle as long as there is one cloud along the line of sight. A more relevant quantity for clumpy media is the probability for an AGN photon to escape unabsorbed. In our sample, type 1s have relatively high escape probabilities, while in type 2s, as expected, tend to be low. Our fits also confirmed that the tori of Seyfert galaxies are compact with torus model radii in the range 1-6pc. The scaling of the models to the data also provided the AGN bolometric luminosities, which were found to be in good agreement with estimates from the literature. When we combined our sample of Seyfert galaxies with a sample of PG quasars from the literature to span a range of L_bol(AGN)~10^{43}-10^{47}erg/s, we found plausible evidence of the receding torus. That is, there is a tendency for the torus geometrical covering factor to be lower at high AGN luminosities than at low AGN luminosities. This is because at low AGN luminosities the tori appear to have wider angular sizes and more clouds along radial equatorial rays. We cannot, however rule out the possibility that this is due to contamination by extended dust structures not associated with the dusty torus at low AGN luminosities, since most of these in our sample are hosted in highly inclined galaxies. (Abridged)Comment: Accepted for publication in Ap

The soft X-ray and narrow-line emission of Mrk573 on kiloparcec scales

We present a study of the circumnuclear region of the nearby Seyfert galaxy Mrk573 using Chandra, XMM-Newton and HST data. The X-ray morphology shows a biconical region extending up to 12 arcsecs (4 kpc) in projection from the nucleus. A strong correlation between the X-rays and the highly ionized gas seen in the [O III] image is reported. Moreover, we have studied the line intensities detected with the RGS/XMM-Newton and used them to fit the low resolution EPIC/XMM-Newton and ACIS/Chandra spectra. The RGS spectrum is dominated by emission lines of C VI, O VII, O VIII, Fe XVII, and Ne IX, among others. A good fit is obtained using these emission lines found in the RGS spectrum as a template for Chandra spectra of the nucleus and extended emission. The photoionization model Cloudy provides a reasonable fit for both the nuclear region and the cone-like structures. For the nucleus the emission is modelled using two phases: a high ionization [log(U)=1.23] and a low ionization [log(U)=0.13]. For the high ionization phase the transmitted and reflected component are in a ratio 1:2, whereas for the low ionization the reflected component dominates. For the extended emission, we successfully reproduced the emission with two phases. The first phase shows a higher ionization parameter for the NW (log(U)=0.9) than for the SE cone (log(U)=0.3). The second phase shows a low ionization parameter (log(U)=-3) and is rather uniform for NW and SE cones. In addition, the nuclear optical/infrared SED has been modeled by a clumpy torus model. The torus bolometric luminosity agrees with the AGN luminosity inferred from the observed hard X-ray spectrum. The optical depth along the line of sight derived from the SED fit indicates a high neutral column density in agreement with the classification of the nucleus as a Compton-thick AGN.Comment: 15 pages, 14 figures, final version of the paper submitted to Ap

Probing the Nuclear and Circumnuclear Activity of NGC1365 in the Infrared

We present new far-infrared (70-500micron) Herschel PACS and SPIRE imaging observations as well as new mid-IR Gemini/T-ReCS imaging (8.7 and 18.3micron) and spectroscopy of the inner Lindblad resonance (ILR) region (R<2.5kpc) of the spiral galaxy NGC1365. We complemented these observations with archival Spitzer imaging and spectral mapping observations. The ILR region of NGC1365 contains a Seyfert 1.5 nucleus and a ring of star formation with an approximate diameter of 2kpc. The strong star formation activity in the ring is resolved by the Herschel/PACS imaging data, as well as by the Spitzer 24micron continuum emission, [NeII]12.81micron line emission, and 6.2 and 11.3micron PAH emission. The AGN is the brightest source in the central regions up to lambda~24micron, but it becomes increasingly fainter in the far-infrared when compared to the emission originating in the infrared clusters (or groups of them) located in the ring. We modeled the AGN unresolved infrared emission with the CLUMPY torus models and estimated that the AGN contributes only to a small fraction (~5%) of the infrared emission produced in the inner ~5kpc. We fitted the non-AGN 24-500micron spectral energy distribution of the ILR region and found that the dust temperatures and mass are similar to those of other nuclear and circumnuclear starburst regions. Finally we showed that within the ILR region of NGC1365 most of the on-going star formation activity is taking place in dusty regions as probed by the 24micron emission.Comment: Accepted for publication in MNRA

Mid-infrared imaging- and spectro-polarimetric subarcsecond observations of NGC 1068

We present sub-arcsecond 7.5$-$13 $\mu$m imaging- and spectro-polarimetric observations of NGC 1068 using CanariCam on the 10.4-m Gran Telescopio CANARIAS. At all wavelengths, we find: (1) A 90 $\times$ 60 pc extended polarized feature in the northern ionization cone, with a uniform $\sim$44$^{\circ}$ polarization angle. Its polarization arises from dust and gas emission in the ionization cone, heated by the active nucleus and jet, and further extinguished by aligned dust grains in the host galaxy. The polarization spectrum of the jet-molecular cloud interaction at $\sim$24 pc from the core is highly polarized, and does not show a silicate feature, suggesting that the dust grains are different from those in the interstellar medium. (2) A southern polarized feature at $\sim$9.6 pc from the core. Its polarization arises from a dust emission component extinguished by a large concentration of dust in the galaxy disc. We cannot distinguish between dust emission from magnetically aligned dust grains directly heated by the jet close to the core, and aligned dust grains in the dusty obscuring material surrounding the central engine. Silicate-like grains reproduce the polarized dust emission in this feature, suggesting different dust compositions in both ionization cones. (3) An upper limit of polarization degree of 0.3 per cent in the core. Based on our polarization model, the expected polarization of the obscuring dusty material is $\lesssim$0.1 per cent in the 8$-$13 $\mu$m wavelength range. This low polarization may be arising from the passage of radiation through aligned dust grains in the shielded edges of the clumps.Comment: 17 pages, 10 figures, accepted for publication at MNRA

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 micron of eighteen Seyfert galaxies, reporting high spatial resolution nuclear fluxes for the entire sample. We construct spectral energy distributions (SEDs) that the AGN dominates adding near-IR measurements from the literature at similar angular resolution. The IR SEDs of intermediate-type Seyferts are flatter and present higher 10 to 18 micron ratios than those of Seyfert 2. We fit the individual SEDs with clumpy torus models using the in-house-developed BayesClumpy tool. The 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, we find that edge-on geometries are more probable than face-on views, with a number of clouds along equatorial rays of N = 5-15. The 10 micron silicate feature is generally modeled in shallow absorption. For the intermediate-type Seyferts, N 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 disc. 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.Comment: 26 pages, 8 figures, 9 tables. Accepted for publication in Ap