Keck Spectropolarimetry of the Radio Galaxy 3C 234

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Session 24 -- AGNs/QSOs - High Luminosity
Display presentation, Tuesday, June 13, 1995, 9:20am - 6:30pm

[24.10] Keck Spectropolarimetry of the Radio Galaxy 3C 234

Hien D. Tran and Marshall H. Cohen (Caltech)

We present high signal-to-noise ratio spectropolarimetric data of 3C 234 observed with the 10 m Keck telescope. The data were obtained with the polarimeter on the Low Resolution Imaging Spectrograph, covering a wavelength range of 3900--9000 \AA~at moderate resolution. They show that broad H$\alpha$, and H$\beta$ are apparently polarized higher than the continuum but at the same position angle perpendicular to the radio axis, similar to the behaviors of many Seyfert 2 galaxies reported by Tran (1995, ApJ, 440, 578). As proposed for the Seyfert 2 galaxies, we interpret the current data in terms of the presence of a second extended continuum, and derive a high 25 \% intrinsic polarization of the hidden continuum and broad emission lines due to scattering. A combination of high extinction experienced by the scattered radiation and dilution by the unreddened extended continuum, which makes up nearly half of the starlight subtracted total flux, causes the slight increase to the red of the polarization after correction for starlight dilution has been applied. Our data show that, free of the obscuring material or from another direction, 3C 234 would appear just like a luminous quasar, thus providing some support for the unification of quasars and radio galaxies. Our observations also suggest that spatially extended continuum in AGNs maybe quite common and thus should be taken into account when their intrinsic nuclear continua are studied.

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