Infrared spectropolarimetry of Seyfert galaxy NGC1068

Although most of the luminosity of Seyfert galaxy nuclei is emitted in the IR, the relative amounts of thermal dust and non-thermal emission are uncertain. Seyfert galaxies generally have smooth and featureless IR spectra, in contrast to the prominent dust emission features seen in galaxies whose nuclei resemble giant H II regions - the star burst nuclei^1,2. Nevertheless, in type 2 Seyferts, the general form of the energy distribution and lack of marked variability suggest that here too thermal dust emission is dominant ^3-5, and in NGC1068 this supposition is supported by the resolved size of its nucleus⁶. Dust is observed in absorption at 10 m (refs 7,8) and in emission near 20 m (ref. 9). Polarization has been detected from the UV to 10 m, and attributed to scattering and absorption at short wavelengths¹⁰ with a possible non-thermal component^11,12, to scattering and non-thermal radiation in the near IR⁹, and to either absorption or non-thermal emission in the 10 m region¹³. We present here spectropolarimetric measurements of NGC1068, between 8 and 13 m, which show that the polarized flux at these wavelengths is intrinsic to the emission mechanism and not due to absorption by aligned grains.