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Astron. Astrophys. 346, 359-368 (1999)


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Two multiple-imaged z = 4.05 galaxies in the cluster-lens Abell 2390 *

R. Pelló 1, J.P. Kneib 1, J.F. LeBorgne 1, J. Bézecourt 1,4, T.M. Ebbels 2, I. Tijera 3, G. Bruzual 5,1, J.M. Miralles 1,6, I. Smail 7, G. Soucail 1 and T.J. Bridges 2,8

1 Observatoire Midi-Pyrénées, UMR 5572, 14 Avenue E. Belin, F-31400 Toulouse, France
2 Institute of Astronomy, Madingley Road, Cambridge CB3 0HA, UK
3 Departament d'Astronomia i Meteorologia, Universitat de Barcelona, Diagonal 648, E-08028 Barcelona, Spain
4 Kapteyn Instituut, P.O. Box 800, 9700 AV Groningen, The Netherlands
5 Centro de Investigaciones de Astronomía (CIDA), Apartado Postal 264, Mérida, Venezuela
6 Astronomical Institute, Tohoku University, Aramaki, Aoba-ku, Sendai 980-8578, Japan
7 Department of Physics, University of Durham, South Road, Durham DH1 3LE, UK
8 Anglo-Australian Observatory, PO Box 296, Epping NSW 1710, Australia

Received 26 October 1998 / Accepted 12 April 1999

Abstract

We present the first results on the identification and study of very distant field galaxies in the core of cluster-lenses, using a selection criterium based on both lens modelling and photometric redshifts. We concentrate on two multiple-imaged sources at [FORMULA] in the cluster Abell 2390. The two objects presented in this paper, namely H3 (cusp arc) and H5 (fold arc), were identified through lens modelling as multiple images of high-redshift sources at [FORMULA] (Kneib et al. 1999). We confirm the excellent agreement between this identification and both their photometric redshifts and morphologies. Our CFHT/WHT program for a systematic redshift survey of arcs in clusters has allowed to obtain a set of spectra on three different images at [FORMULA]: the brightest image of H3, whose redshift was already confirmed by Frye & Broadhurst (1998), and the two brightest images of H5. The later is then confirmed spectroscopically as a multiple image, giving a strong support to the lens model. The main feature in each of these spectra is a strong emission line, identified as Ly [FORMULA], leading to [FORMULA] for both H3 and H5. The spectrophotometric properties of these galaxies are studied, in particular the degeneracy in the parameter-space defined by the SFR type, age, metallicity and reddening. H3 and H5 are intrinsically bright and clumpy galaxies ([FORMULA] to [FORMULA] -2 magnitudes), located [FORMULA] kpc apart on the source plane, with mean metallicities compatible with a fraction of solar or even solar values. These results seem to favour a hierarchical merging scenario, where we are seeing a relatively evolved phase in these two [FORMULA] objects, with stars forming locally and efficiently.

Key words: galaxies: clusters: general – galaxies: clusters: individual: – cosmology: observations – cosmology: dark matter – cosmology: gravitational lensing

* Based on observations collected with the Canada-France-Hawaii Telescope (CFHT), the William Herschel Telescope (WHT) and the Hubble Space Telescope (HST).

Send offprint requests to: R. Pelló (roser@obs-mip.fr)

© European Southern Observatory (ESO) 1999

Online publication: May 21, 1999

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