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

R. Pello·J. -P. Kneib·J. -F. Le Borgne·J. Bezecourt·T. M. Ebbels·I. Tijera·G. Bruzual·J. M. Miralles·I. Smail·G. Soucail·T. J. Bridges
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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 z=4.05 in the cluster A2390. The 2 objects presented in this paper, namely H3 and H5, were identified through lens modelling as multiple images of high-redshift sources at z>3.5. 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 3 different images at z~4: the brightest image of H3, which 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-alpha, leading to z=4.05 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 sources located ~100 kpc part on the source plane, with mean metallicities compatible with a fraction of solar or even solar values. All these results seem to favour a hierarchical merging scenario, where we are actually seeing a relatively advanced step for these 2 z~4 objects, with stars forming locally and efficiently from a preenriched gas.

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R. Pello, J. -P. Kneib, J. -F. Le Borgne, J. Bezecourt, T. M. Ebbels, I. Tijera, G. Bruzual, J. M. Miralles, I. Smail, G. Soucail, T. J. Bridges. 1999-04-14. Two multiple-imaged z=4.05 galaxies in the cluster-lens Abell 2390. https://arxiv.org/abs/astro-ph/9810390

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