Discovery of a high-redshift Einstein ring

Free access article

Issue		A&A Volume 436, Number 2, June III 2005


Page(s)		L21 - L25
Section		Letters
DOI		http://dx.doi.org/10.1051/0004-6361:200500115

A&A 436, L21-L25 (2005)
DOI: 10.1051/0004-6361:200500115

Letter

Discovery of a high-redshift Einstein ring

R. A. Cabanac^{1, 2, 3}, D. Valls-Gabaud^{3, 4}, A. O. Jaunsen², C. Lidman² and H. Jerjen⁵

¹ Dep. de Astronomía y Astrofísica, Pontificia Universidad Católica de Chile, Casilla 306, Santiago, Chile
e-mail: cabanac@cfht.hawaii.edu
² European Southern Observatory, Alonso de Cordova 3107, Casilla 19001, Santiago, Chile
³ Canada-France-Hawaii Telescope, 65-1238 Mamalahoa Highway, Kamuela, HI 96743, USA
⁴ CNRS UMR 5572, LATT, Observatoire Midi-Pyrénées, 14 Av. E. Belin, 31400 Toulouse, France
⁵ Research School of Astronomy and Astrophysics, ANU, Mt. Stromlo Observatory, Weston ACT 2611, Australia

(Received 24 December 2004 / Accepted 26 April 2005)

Abstract
We report the discovery of a partial Einstein ring of radius 1 $\farcs$ 48 produced by a massive (and seemingly isolated) elliptical galaxy. The spectroscopic follow-up at the VLT reveals a 2 $L_\star$ galaxy at z=0.986, which is lensing a post-starburst galaxy at z=3.773. This unique configuration yields a very precise measure of the mass of the lens within the Einstein radius, $(8.3 \pm 0.4) \times 10^{11}$ h₇₀^-1 $M_{\odot}$ . The fundamental plane relation indicates an evolution rate of ${\rm d}$ $\log (M/L)_{B} / {\rm d}z = -0.57\pm0.04$ , similar to other massive ellipticals at this redshift. The source galaxy shows strong interstellar absorption lines indicative of large gas-phase metallicities, with fading stellar populations after a burst. Higher resolution spectra and imaging will allow the detailed study of an unbiased representative of the galaxy population when the universe was just 12% of its current age.

Key words: cosmology: observations -- gravitational lensing -- galaxies: high-redshift -- ellipticals -- evolution -- FOR J0332-3557

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