Polarized Broad‐Line Emission from Low‐Luminosity Active Galactic Nuclei

In order to determine whether unified models of active galactic nuclei applyto low-luminosity objects, we have undertaken a spectropolarimetric survey ofof LINERs and Seyfert nuclei at the Keck Observatory. The 14 objects observedhave a median H-alpha luminosity of 8x10^{39} erg/s, well below the typicalvalue of ~10^{41} erg/s for Markarian Seyfert nuclei. Polarized broad H-alphaemission is detected in three LINERs: NGC 315, NGC 1052, and NGC 4261. Each ofthese is an elliptical galaxy with a double-sided radio jet, and theemission-line polarization in each case is oriented roughly perpendicular tothe jet axis, as expected for the obscuring torus model. NGC 4261 and NGC 315are known to contain dusty circumnuclear disks, which may be the outerextensions of the obscuring tori. The detection of polarized broad-lineemission suggests that these objects are nearby, low-luminosity analogs ofobscured quasars residing in narrow-line radio galaxies. The nuclear continuumof the low-luminosity Seyfert 1 galaxy NGC 4395 is polarized at p = 0.67%,possibly the result of an electron scattering region near the nucleus.Continuum polarization is detected in other objects, with a median level of p =0.36% over 5100-6100 A, but in most cases this is likely to be the result oftransmission through foreground dust. The lack of significant broad-linepolarization in most type 1 LINERs is consistent with the hypothesis that weview the broad-line regions of these objects directly, rather than in scatteredlight.Comment: 28 pages, including 3 tables and 16 figures. Uses the emulateapj latex style file. Accepted for publication in The Astrophysical Journa