TY - JOUR
T1 - The origin of the mid-infrared nuclear polarization of active galactic nuclei
AU - Lopez-Rodriguez, E.
AU - Alonso-Herrero, A.
AU - Diaz-Santos, T.
AU - Gonzalez-Martin, O.
AU - Ichikawa, K.
AU - Levenson, N. A.
AU - Martinez-Paredes, M.
AU - Nikutta, R.
AU - Packham, C.
AU - Perlman, E.
AU - Ramos Almeida, C.
AU - Rodriguez-Espinosa, J. M.
AU - Telesco, C. M.
N1 - Funding Information:
The referee is especially thanked for a thorough reading of the original submitted paper, and making numerous useful comments to improve it. Based on observations made with the GTC, installed in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias, in the island of La Palma. A.A.H. acknowledges financial support from the Spanish Ministry of Economy and Competitiveness through the Plan Nacional de Astronomía y Astrofísica under grant AYA2015-64346-C2-1-P, which is partly funded by the FEDER programme. O.G.M. acknowledges financial support from the UNAM PAPIIT IA100516 and IA103118. C.R.A. acknowledges the Ramón y Cajal Program of the Spanish Ministry of Economy and Competitiveness through project RYC-2014-15779 and the Spanish Plan Nacional de Astronomía y Astrofisíca under grant AYA2016-76682-C3-2-P. K.I. acknowledges the financial support by the Grant-in-Aid for JSPS fellow for young researchers (PD). C.P. acknowledges financial support from NSF-1616828. Analysis done with ASTROPY1 routines.
PY - 2018/8/1
Y1 - 2018/8/1
N2 - We combine new (NGC 1275, NGC 4151, and NGC 5506) and previously published (Cygnus A, Mrk 231, and NGC 1068) sub-arcsecond resolutionmid-infrared (MIR; 8-13 μm) imagingand spectro-polarimetric observations of six Seyfert galaxies using CanariCam on the 10.4-m Gran Telescopio CANARIAS. These observations reveal a diverse set of physical processes responsible for the nuclear polarization, and permit characterization of the origin of the MIR nuclear polarimetric signature of active galactic nuclei (AGN). For all radio-quiet objects, we found that the nuclear (<10 pc) polarization is low(<1 per cent), and the degree of polarization is often a few per cent over extended regions of the host galaxy where we have sensitivity to detect such extended emission (i.e. NGC 1068 and NGC 4151). We suggest that the higher degree of polarization previously found in lower resolution data arises only on the larger-thannuclear scales (few hundred of pc). Only the radio-loud Cygnus A exhibits significant nuclear polarization (~11 per cent), attributable to synchrotron emission from the pc-scale jet close to the core. We present polarization models that suggest that the MIR nuclear polarization for highly obscured objects arises from a self-absorbed MIR-polarized clumpy torus and/or dichroism from the host galaxy, while for unabsorbed cores,MIR polarization arises from dust scattering in the torus and/or surrounding nuclear dust.
AB - We combine new (NGC 1275, NGC 4151, and NGC 5506) and previously published (Cygnus A, Mrk 231, and NGC 1068) sub-arcsecond resolutionmid-infrared (MIR; 8-13 μm) imagingand spectro-polarimetric observations of six Seyfert galaxies using CanariCam on the 10.4-m Gran Telescopio CANARIAS. These observations reveal a diverse set of physical processes responsible for the nuclear polarization, and permit characterization of the origin of the MIR nuclear polarimetric signature of active galactic nuclei (AGN). For all radio-quiet objects, we found that the nuclear (<10 pc) polarization is low(<1 per cent), and the degree of polarization is often a few per cent over extended regions of the host galaxy where we have sensitivity to detect such extended emission (i.e. NGC 1068 and NGC 4151). We suggest that the higher degree of polarization previously found in lower resolution data arises only on the larger-thannuclear scales (few hundred of pc). Only the radio-loud Cygnus A exhibits significant nuclear polarization (~11 per cent), attributable to synchrotron emission from the pc-scale jet close to the core. We present polarization models that suggest that the MIR nuclear polarization for highly obscured objects arises from a self-absorbed MIR-polarized clumpy torus and/or dichroism from the host galaxy, while for unabsorbed cores,MIR polarization arises from dust scattering in the torus and/or surrounding nuclear dust.
KW - Galaxies: Seyfert
KW - Galaxies: individual: Cygnus A
KW - Galaxies: nuclei
KW - Methods: observational
KW - Mrk 231
KW - NGC 1068
KW - NGC 1275
KW - NGC 4151
KW - NGC 5506
KW - Techniques: high angular resolution
KW - Techniques: polarimetric
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U2 - 10.1093/MNRAS/STY1197
DO - 10.1093/MNRAS/STY1197
M3 - Article
AN - SCOPUS:85049982955
VL - 478
SP - 2350
EP - 2358
JO - Monthly Notices of the Royal Astronomical Society
JF - Monthly Notices of the Royal Astronomical Society
SN - 0035-8711
IS - 2
ER -