Other
Scientific paper
Jan 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994apjs...90....1e&link_type=abstract
Astrophysical Journal Supplement Series, vol. 90, no. 1, p. 1-30
Other
267
Accretion Disks, Active Galactic Nuclei, Astronomical Models, Demography, Emission Spectra, H Alpha Line, Line Shape, Quasars, Radio Galaxies, Red Shift, Relativistic Effects, Taxonomy, Astronomical Observatories, Calibrating, Charge Coupled Devices, Near Infrared Radiation, Spectral Line Width, Spectroscopic Telescopes
Scientific paper
We present the results of a comprehensive study of the broad H alpha 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 H alpha profiles that can be fitted by a simple relativistic disk model, bringing the total number of such profiles to 12. Disklike 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 H alpha full width at half-maximum twice as large as the remainder of the sample (12,500 km/sec vs. 5700 km/sec), (2) optical continuum around H alpha consisting of 20%-100% starlight, versus less than 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 disklike emitters are argued to be intrinsic. For the entire sample of radio-loud objects, the broad H alpha lines at half-maximum are preferentially redshifted with respect to the narrow lines by (Delta lambda/lambda)=(6 +/- 2) x 10-4 on average, which corresponds to Keplerian motion at a radius of approximately 2500 GM/c2 if interpreted as gravitational plus transverse redshift. This result is entirely consistent with previous studies of H beta, which find more redshifts in radio-loud objects, but equal numbers of blueshifts and redshifts in radio-loud samples, but equal numbers of blueshifts and redshifts in optically selected samples. Thus, in radio-loud objects, the Balmer-line emitting gas is more likely to be dominated by gravitational motion close to the black hole than in radio-quiet objects. It appears that the disklike profiles are better fitted by small inclination angles. Although contrary to the conventional interpretation of the broadest emission lines in radio-loud active galactic nuclei (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. We obtained new (secure) redshifts for five objects which had incorrect values in the literature.
Eracleous Michael
Halpern Jules P.
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