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Published April 1, 1996 | Published
Journal Article Open

1608+656: A Gravitationally Lensed PostStarburst Radio Galaxy

Abstract

The gravitational lens system 1608+656 displays four flat-spectrum, pointlike components that are the images of the unresolved core of a double-lobed radio source. The lensing mass is a galaxy at z = 0.630. New spectra of this system enable us to determine a conclusive redshift of 1.394 for the lensed object. The spectra show prominent high-order Balmer absorption lines and Mg II absorption. These lines, and the absence of [O II] emission, indicate that this is a poststarburst or E + A galaxy. It is unique among lensed objects in not being a quasar and among E + A galaxies in having the highest known redshift. Even allowing for lens magnification, the lensed object is a very luminous galaxy, with an absolute magnitude, M(r) = -22.8 mag. The deconvolved infrared image indicates that the galaxy may be slightly resolved. The radio luminosity density of the lobes is L_(1.4) = 5.78 × 10^(25) W Hz^(-1), which puts the source on the boundary between FR I and FR II radio galaxies. Together with the redshift for the lens and a satisfactory mass model, the determination of the lensed object redshift makes this system an excellent candidate for measuring H_0.

Additional Information

© The American Astronomical Society. Received 5 December 1995; accepted 17 January 1996. For valuable discussions, we thank Roger Blandford, David Hogg, Steve Myers, Ann Zabludoff, Neal Jackson, and Lee Armus. We are grateful to Greg Taylor for helping with the optical observations. We thank the staff at Palomar Observatory for their assistance during our observing runs. CLASS and Infrared astrophysics at Caltech are supported by grants from the NSF. C. D. F. is supported by a NSF Graduate Research Fellowship. D. S. W. acknowledges support of a Hubble Fellowship provided by NASA through grant HF-1040.01-92A from the STScl, which is operated by AURA.

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August 20, 2023
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