No abstract

Strong infrared circular polarization resulting from dust scattering in reflection nebulae in the Orion OMC-1 star-formation region has been observed. Circular polarization at shorter wavelengths might have been important in inducing chiral asymmetry in interstellar organic molecules that could be subsequently delivered to the early Earth by comets, interplanetary dust particles, or meteors. This could account for the excess of L-amino acids found in the Murchison meteorite and could explain the origin of the homochirality of biological molecules.

We present optical spectropolarimetry of the nuclei of 36 Seyfert 1 galaxies, obtained with the William Herschel and the Anglo-Australian Telescopes from 1996 to 1999. In 20 of these, the optical emission from the active nucleus is intrinsically polarized. We have measured a significant level of polarization in a further seven objects but these may be heavily contaminated by Galactic interstellar polarization. The intrinsically polarized Seyfert 1 galaxies exhibit a variety of characteristics, with the average polarization ranging from <0.5 to 5 per cent and with many showing variations in both the degree and position angle of polarization across the broad Hα emission line. We identify a small group of Seyfert 1 galaxies that exhibit polarization properties similar to those of Seyfert 2 galaxies in which polarized broad lines have been discovered. These objects represent direct observational evidence that a Seyfert 2-like far-field polar scattering region is also present in Seyfert 1 galaxies. Several other objects have features that can be explained in terms of equatorial scattering of line emission from a rotating disc. We propose that much of the diversity in the polarization properties of Seyfert galaxies can be understood in terms of a model involving both equatorial and polar scattering, the relative importance of the two geometries as sources of polarized light being determined principally by the inclination of the system axis to the line of sight.

We report the detection of linear polarization from Sgr A* at 750, 850, 1350, and 2000 µm which confirms the contribution of synchrotron radiation. From the lack of polarization at longer wavelengths, it appears to arise in the millimeter/submillimeter excess. There are large position angle changes between the millimeter and submillimeter results, and these are discussed in terms of a polarized dust contribution in the submillimeter and various synchrotron models. In the model that best explains the data, the synchrotron radiation from the excess is self-absorbed in the millimeter region and becomes optically thin in the submillimeter. This implies that the excess arises in an extremely compact source of approximately 2 Schwarzschild radii.