Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995aj....110.2597t&link_type=abstract
Astronomical Journal v.110, p.2597
Astronomy and Astrophysics
Astronomy
33
Galaxies: Individual: 3C 234, Galaxies: Seyfert, Techniques: Polarimetric
Scientific paper
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 Spectrometer, covering a wavelength range of 3900-9000A at moderate resolution. They show that broad Hα and Hβ are apparently polarized higher than the adjacent continuum but at the same position angle perpendicular to the radio axis, similar to the behavior of many Seyfert 2 galaxies reported by Tran. 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 for the hidden continuum and broad emission lines, due to scattering. We are able to decompose the observed spectrum of 3C 234 into at least three components comprising: (a) a scattered (polarized) continuum plus broad emission lines from the obscured active galactic nucleus, (b) an extended, unpolarized continuum plus narrow emission lines resembling a typical narrow-line radio galaxy spectrum, and c) a stellar component from the underlying host galaxy. 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-corrected 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 be a luminous quasar, thus providing support for the unification of quasars and radio galaxies. These and other observations suggest that spatially extended continuum in AGNs may be quite common and thus should be taken into account when their intrinsic nuclear continua are studied.
Cohen Marshall H.
Goodrich Robert W.
Tran Hien D.
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