We present high-angular (0.17-0.35 arcsec) resolution imaging polarimetric observations of Mrk 231 in the 3.1 μm filter using MMT-Pol on the 6.5-m MMT, and in the 8.7, 10.3, and 11.6 μm filters using CanariCam on the 10.4-m Gran Telescopio CANARIAS. In combination with already published observations, we compile the 1-12 μm total and polarized nuclear spectral energy distribution (SED). The total flux SED in the central 400 pc is explained as the combination of (1) a hot (731 ± 4 K) dusty structure, directly irradiated by the central engine, which is at 1.6 ± 0.1 pc away and attributed to be in the pc-scale polar region, (2) an optically-thick, smooth and disc-like dusty structure ('torus') with an inclination of 48° ± 23° surrounding the central engine, and (3) an extinguished (AV = 36 ± 5 mag) starburst component. The polarized SED decreases from 0.77 ± 0.14 per cent at 1.2 μm to 0.31 ± 0.15 per cent at 11.6 μm and follows a power-law function, λ~0.57. The polarization angle remains constant (~108°) in the 1-12 μm wavelength range. The dominant polarization mechanism is explained as scattering-off hot dust grains in the pc-scale polar regions.
Bibliographical noteFunding Information:
We would like to thank Dr Chiara Feruglio for their useful comments, which improved the paper significantly. Based on observations made with the GTC, installed in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrof?sica de Canarias, in the island of La Palma. Based on observations made with MMT-Pol on the 6.5-m MMT. CP acknowledge support from the University of Texas at San Antonio. CP acknowledges support from NSF-0904421 grant. CP and TJJ acknowledge support from NSF-0704095 grant. AA-H acknowledges financial support from the Spanish Plan Nacional de Astronom?a y Astrofis?ca under grant AYA2012-31447, which is partly funded by the FEDER program, and financial support from the Spanish Ministry of Economy and Competitiveness (MINECO) under the 2011 Severo Ochoa Program MINECO SEV-2011-0187. PE from grant AYA2012-31277, and LC from grant AYA2012-32295. CRA acknowledges the Ramn y Cajal Program of the Spanish Ministry of Economy and Competitiveness (RYC-2014-15779). NAL is supported by the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., on behalf of the international Gemini partnership of Argentina, Brazil, Canada, Chile, and the USA. RN acknowledges support by FONDECYT grant No. 3140436
© 2016 The Authors.
- Galaxies: Seyfert
- Galaxies: active
- Infrared: galaxies
- Techniques: high angular resolution
- Techniques: polarimetric