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

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 <sup>2,8

1</sup> 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 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 (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 : 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 , leading to 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 ( to -2 magnitudes), located 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 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)

SIMBAD Objects

Contents

• 1. Introduction
• 2. Observational data
  • 2.1. Photometry
  • 2.2. Spectroscopy
• 3. Photometric and spectroscopic study of H3 and H5
  • 3.1. Lensing properties, spectral energy distribution and morphology of the sources
  • 3.2. The photometric redshift approach
• 4. Constraining the stellar population in H3 and H5
• 5. Discussion and conclusions
• Acknowledgements
• References

© European Southern Observatory (ESO) 1999

Online publication: May 21, 1999
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