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UM 425 - A new gravitational lens candidate

Meylan, G. and Djorgovski, S. (1989) UM 425 - A new gravitational lens candidate. Astrophysical Journal, 338 . L1-L4. ISSN 0004-637X. doi:10.1086/185386.

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We report the discovery of a probable new gravitational lens, associated with the quasar UM 425 = QSO 1120 + 019. This object was specifically selected in an optical imaging survey for gravitational lenses because of its relatively high redshift and apparently high luminosity. Multicolor (BVR) images were obtained with a charge-coupled device (CCD) at the Cerro Tololo Interamerican Observatory (CTIO) 60 inch (1.5 m) telescope in 1987 March, showing three close companions around the bright image of the quasar. The follow-up spectroscopy in marginal weather conditions, with the Mount Palomar 200 inch (5 m) and Las Campanas 100 inch (2.5 m) telescopes (in 1988 March and April), suggested that the brightest companion has the same emission lines as the quasar. Additional spectra and additional imaging were obtained with the European Southern Observatory (ESO) 3.6 m telescope at La Silla, in 1988 May. UM 425 and its brightest companion (which we denote as components A and B) have similar BVR colors. Spectra of both objects, in the range 3600-8000 Å, with resolution of about 7 Å pixel^(-1), show the same emission lines, i.e., C IV 1549, C III] 1909, and Mg II 2799, with the same redshift z = 1.465 ± 0.005. The spectra are also similar in shape and in some details, including, possibly some associated absorption in the Mg II 2799 and C IV 1549 lines. The velocity difference between the two brightest components from the cross-correlation technique is ΔV(A-B) = 200 ± 100 km s^(-1) and is consistent with zero. Subtracting a scaled spectrum of the brighter component (A) from that of the brightest companion (B), leaves a residual which may be interpreted as the spectrum of a lensing galaxy at z ≃ 0.6. Whereas we cannot exclude the possibility that we are seeing a pair of physically distinct AGNs, the overall data are in favor of the gravitational lens hypothesis.

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Djorgovski, S.0000-0002-0603-3087
Additional Information:© 1989 American Astronomical Society. Provided by the NASA Astrophysics Data System. Received 1988 August 16; accepted 1988 December 6. Based on observations collected at the European Southern Observatory, Cerro Tololo Interamerican Observatory, Las Campanas Observatory, and Palomar Observatory. It is a pleasure to thank the staff of all observatories involved, and especially H. Pedersen and J. Miranda at ESO, J. Bravo and M. Navarete at CTIO, W. Kunkel and P. Schechter at Las Campanas, and J. Carrasco and D. Tennant at Palomar.Many thanks also to R. Perley for obtaining and reducing the VLA snapshots, and to several colleagues who forced us to reexamine the removal of the atmospheric absorption from the spectra. S. D. acknowledges a partial support from California Institute of Technology and Alfred P. Sloan Foundation.
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Alfred P. Sloan FoundationUNSPECIFIED
Subject Keywords:gravitational lenses — quasars
Record Number:CaltechAUTHORS:20190807-074238924
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:97688
Deposited By: Tony Diaz
Deposited On:07 Aug 2019 16:28
Last Modified:16 Nov 2021 17:33

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