Double-peaked emission lines are found in about 10% of radio objects and their hosts are a reasonably homogeneous class. These exotic line profiles provide (potentially) the most direct, dynamical evidence for the presence of accretion disks in AGNs, although alternative interpretations are also possible. The direction and magnitude of the polarization of the broad lines constitute independent probes of the geometry of the line-emitting region and can serve as tests of competing scenarios for the origin of the lines. In the accretion disk model, for example, the broad Balmer lines of these objects should be polarized about a percent for estimated average disk inclination angles. The polarized line profile can differ significantly from the total flux profile because of the effects of relativistic aberration on viewing angle over the surface of the disk; thus the relative heights of the two peaks in polarized flux can differ from that in the total flux. We report the results of sensitive spectropolarimetric observations of the Hα lines of three of the brightest double-peaked emitters (3C 445, 3C 390.3, and 3C 382) carried out at Lick Observatory, in order to evaluate the merits of the accretion disk interpretation. All three galaxies exhibit some polarization, and structure across the Hα line profile in polarized flux is clearly evident. We will present the spectropolarimetric analysis of the Hα line polarization, and compare the data with recent models of line emitting disks.
American Astronomical Society Meeting Abstracts
- Pub Date:
- December 1996