We present high-angular (0.17$-$0.35 arcsec) resolution imaging polarimetric observations of Mrk 231 in the 3.1 $mu$m filter using MMT-Pol on the 6.5-m MMT, and in the 8.7 $mu$m, 10.3 $mu$m, and 11.6 $mu$m filters using CanariCam on the 10.4-m Gran Telescopio CANARIAS. In combination with already published observations, we compile the 1$-$12 $mu$m 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 $pm$ 4 K) dusty structure, directly irradiated by the central engine, which is at 1.6 $pm$ 0.1 pc away and attributed to be in the pc-scale polar region, 2) an optically-thick, smooth and disk-like dusty structure (`torus) with an inclination of 48 $pm$ 23$^{circ}$ surrounding the central engine, and 3) an extinguished (A$_{mbox{V}} =$ 36 $pm$ 5 mag) starburst component. The polarized SED decreases from 0.77 $pm$ 0.14 per cent at 1.2 $mu$m to 0.31 $pm$ 0.15 per cent at 11.6 $mu$m and follows a power-law function, $lambda^{sim0.57}$. The polarization angle remains constant ($sim$108$^{circ}$) in the 1$-$12 $mu$m wavelength range. The dominant polarization mechanism is explained as scattering off hot dust grains in the pc-scale polar regions.
Download