Discovery of a high-redshift Einstein ring

We report the discovery of a partial Einstein ring of radius 1.''48 produced by a massive (and seemingly isolated) elliptical galaxy. The spectroscopic follow-up at the VLT reveals a 2L(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 +/- 0.4) x 10(11)h(70)(-1) M-circle dot. The fundamental plane relation indicates an evolution rate of dlog(M/L)(B)/dz = -0.57 +/- 0.04, similar to other massive ellipticals at this redshift. The source galaxy shows strong interstellar absorption lines indicative of large gas-phase metallicities, with fading st phase populations after a burst stellar Higher resolution spectra and will allow the detailed imaging study of an unbiased representative of the galaxy population when the universe was just 12% of its current age.