Other
Scientific paper
Dec 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992aas...18110606e&link_type=abstract
American Astronomical Society, 181st AAS Meeting, #106.06D; Bulletin of the American Astronomical Society, Vol. 24, p.1292
Other
Scientific paper
We present the results of a comprehensive study of the broad Hα emission lines of radio galaxies and radio-loud quasars. The data consist of 74 new spectra plus information drawn from 20 spectra in the literature. The principal result is the discovery of eight new double-peaked Hα profiles that can be fitted by a simple relativistic disk model, bringing the total number of such profiles to 12. Disk-like emitters comprise 10% of radio-loud objects in our representative sample, and arguably constitute a new ``class'' on the basis of the following additional properties which they possess: (1) average Hα FWHM twice as large as the remainder of the sample (12,500 km s(-1) vs 5,700 km s(-1) ), (2) optical continuum around Hα consisting of 20--100% starlight, vs <20% for the other objects, (3) large equivalent widths of low-ionization forbidden lines ([O I] and [S II]), and (4) large [O I]/[O III] ratios. The properties of the disk-like emitters are argued to be intrinsic, since they are not extensions of any of the known correlations which are thought to represent viewing angle effects in several unifying schemes for radio-loud objects. Neither are there any radio-quiet counterparts of this class. The Chen and Halpern model, in which the inner disk is an ion-supported torus which illuminates the outer disk with a hard ionizing continuum, goes a long way toward explaining the properties of disk-like emitters, and why they are best recognized in Hα . The applicability of other models, such as supermassive binary black holes, jets, and other radial flows, are also evaluated for disk-like profiles and other objects in our sample. Although we neither support nor contradict unifying models based on viewing direction, it appears that the disk-like profiles are better fitted by small inclination angles. Although contrary to the conventional interpretation of the broadest emission lines in radio-loud AGNs, this is to be expected for an accretion disk origin. A number of reasons are suggested for this possible selection effect, with the consequence that the accretion disk could contribute at least partially to the Balmer lines of significantly more objects than just the 10% which are obvious.
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