Polarized broad-line emission from low-luminosity active galactic nuclei

In order to determine whether unified models of active galactic nuclei appl y to low-luminosity objects, we have undertaken a spectropolarimetric surve y of LINERs and Seyfert nuclei at the Keck Observatory. The 14 objects obse rved have a median Ha luminosity of 8 x 10(39) ergs s(-1), well below the t ypical value of similar to 10(41) ergs s(-1) for Markarian Seyfert nuclei. Polarized broad Ha emission is detected in three LINERs: NGC 315, NGC 1052, and NGC 4261. Each of these is an elliptical galaxy with a double-sided ra dio jet, and the emission-line polarization in each case is oriented roughl y perpendicular to the jet axis, as expected for the obscuring torus model. NGC 4261 and NGC 315 are known to contain dusty circumnuclear disks, which may be the outer extensions of the obscuring tori. The detection of polari zed broad-line emission suggests that these objects are nearby, low-luminos ity analogs of obscured quasars residing in narrow-line radio galaxies. The nuclear continuum of the low-luminosity Seyfert 1 galaxy NGC 4395 is polar ized at p = 0.67%, possibly the result of an electron-scattering region nea r the nucleus. Continuum polarization is detected in other objects, with a median level of p = 0.36% over 5100-6100 Angstrom, but in most cases this i s likely to be the result of transmission through foreground dust. The lack of significant broad-line polarization in most type 1 LINERs is consistent with the hypothesis that we view the broad-line regions of these objects d irectly, rather than in scattered light.