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The “Gravitational Lens” 3C 321: A Remarkable Impostor

Published online by Cambridge University Press:  19 July 2016

Alexei V. Filippenko
Alexei V. Filippenko*
Affiliation:
Department of Astronomy, University of California, Berkeley, CA 94720 USA

Abstract

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Recent observations of the radio galaxy 3C 321 are presented. The optical nucleus consists of two components (A, B), separated by ∼ 4″ (∼ 6 kpc), whose low-resolution spectra strongly resemble those of high-ionization type 2 Seyfert nuclei. The relative intensities of the emission lines differ in A and B by less than 1%, and their profiles are almost identical. 3C 321 appears to be a convincing example of a gravitationally lensed object.

Careful analysis of high-quality radio and optical data, however, reveals that the system is almost certainly not a lens. The equivalent widths of the emission lines are roughly twice as high in B than in A, and there are significant spatial offsets between regions of bright continuum and line emission. A slight, but fundamental, difference is visible in the two Hα emission profiles. The radial velocities of A and B are discrepant by 31 ± 10 km s−1. Finally, component A is nearly coincident with a flat-spectrum radio core, whereas B is next to an extended, steep-spectrum knot of radio emission.

This object should serve as a warning to lens hunters: beware of impostors, whose true properties may be difficult to ascertain without extensive optical and radio observations.

Type
Chapter XIII: Gravitational Lenses
Information
Symposium - International Astronomical Union , Volume 124: Observational Cosmology , 1987 , pp. 761 - 765
Copyright
Copyright © Reidel 1987 

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