Examinando por Autor "Packham, C."

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Acceso Abierto
ALMA Polarimetry Measures Magnetically Aligned Dust Grains in the Torus of NGC 1068
(The Institute of Physics (IOP), 2020-04-14) López Rodríguez, E.; Alonso Herrero, A.; García Burillo, S.; Gordon, M. S.; Ichikawa, K.; Imanishi, M.; Kameno, S.; Levenson, N. A.; Nikutta, R.; Packham, C.; https://creativecommons.org/licenses/by-nc-nd/4.0/; National Aeronautics and Space Administration (NASA); Agencia Estatal de Investigación (AEI); 0000-0001-5357-6538; 0000-0002-1913-2682; 0000-0002-4377-903X; 0000-0001-6186-8792; 0000-0002-5158-0063; Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737
The obscuring structure surrounding active galactic nuclei (AGN) can be explained as a dust and gas flow cycle that fundamentally connects the AGN with their host galaxies. This structure is believed to be associated with dusty winds driven by radiation pressure. However, the role of magnetic fields, which are invoked in almost all models for accretion onto a supermassive black hole and outflows, has not been thoroughly studied. Here we report the first detection of polarized thermal emission by means of magnetically aligned dust grains in the dusty torus of NGC 1068 using ALMA Cycle 4 polarimetric dust continuum observations (007, 4.2 pc; 348.5 GHz, 860 mu m). The polarized torus has an asymmetric variation across the equatorial axis with a peak polarization of 3.7% 0.5% and position angle of 109 degrees 2 degrees (B-vector) at similar to 8 pc east from the core. We compute synthetic polarimetric observations of magnetically aligned dust grains assuming a toroidal magnetic field and homogeneous grain alignment. We conclude that the measured 860 mu m continuum polarization arises from magnetically aligned dust grains in an optically thin region of the torus. The asymmetric polarization across the equatorial axis of the torus arises from (1) an inhomogeneous optical depth and (2) a variation of the velocity dispersion, i.e., a variation of the magnetic field turbulence at subparsec scales, from the eastern to the western region of the torus. These observations and modeling constrain the torus properties beyond spectral energy distribution results. This study strongly supports that magnetic fields up to a few parsecs contribute to the accretion flow onto the active nuclei.
Acceso Abierto
Torus model properties of an ultra-hard X-ray selected sample of Seyfert galaxies
(Oxford Academics: Oxford University Press, 2019-04-10) García Bernete, I.; Ramos Almeida, C.; Alonso Herrero, A.; Ward, M. J.; Acosta Pulido, J. A.; Pereira Santaella, M.; Hernán Caballero, A.; Asensio Ramos, A.; González Martín, O.; Levenson, N. A.; Mateos, S.; Carrera, F. J.; Ricci, C.; Roche, P. F.; Márquez, I.; Packham, C.; Masegosa, J.; Fuller, L.; Agencia Estatal de Investigación (AEI); Science and Technology Facilities Council (STFC); Ministerio de Economía y Competitividad (MINECO); Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737
We characterize for the first time the torus properties of an ultra-hard X-ray (14–195 keV) volume-limited (DL < 40 Mpc) sample of 24 Seyfert (Sy) galaxies (BCS40 sample). The sample was selected from the Swift/BAT nine-month catalogue. We use high angular resolution nuclear infrared (IR) photometry and N-band spectroscopy, the CLUMPY torus models and a Bayesian tool to characterize the properties of the nuclear dust. In the case of the Sy1s, we estimate the accretion disc contribution to the subarcsecond resolution nuclear IR SEDs (∼0.4 arcsec) which is, on average, 46 ± 28, 23 ± 13, and 11 ± 5 per cent in the J, H, and K bands, respectively. This indicates that the accretion disc templates that assume a steep fall for longer wavelengths than 1 μm might underestimate its contribution to the near-IR emission. Using both optical (broad versus narrow lines) and X-ray (unabsorbed versus absorbed) classifications, we compare the global posterior distribution of the torus model parameters. We confirm that Sy2s have larger values of the torus covering factor (CT ∼ 0.95) than Sy1s (CT ∼ 0.65) in our volume-limited Seyfert sample. These findings are independent of whether we use an optical or X-ray classification. We find that the torus covering factor remains essentially constant within the errors in our luminosity range and there is no clear dependence with the Eddington ratio. Finally, we find tentative evidence that even an ultra-hard X-ray selection is missing a significant fraction of highly absorbed type 2 sources with very high covering factor tori.