Spectroscopy of the optical Einstein ring 0047-2808

We present optical and near-infrared spectroscopic observations of the optical Einstein ring 0047 - 2808. We detect both [O III] lines lambda lambda 4959, 5007 near similar to 2.3 mu m, confirming the redshift of the lensed source as z = 3.595. The Ly alpha line is redshifted relative to the [O III] line by 140 +/- 20 km s(-1). Similar velocity shifts have been seen in nearby starburst galaxies. The [O III] line is very narrow, 130 km s(-1) FWHM. If the ring is the image of the centre of a galaxy, the one-dimensional stellar velocity dispersion sigma = 55 km s(-1) is considerably smaller than the value predicted by Baugh et al. for the somewhat brighter Lyman-break galaxies, The Ly alpha line is significantly broader than the [O III] line, probably due to resonant scattering. The stellar central velocity dispersion of the early-type deflector galaxy at z = 0.485 is 250 +/- 30 km s(-1) This value is in good agreement both with the value predicted from the radius of the Einstein ring (and a singular isothermal sphere model for the deflector), and with the value estimated from the D-n-sigma relation.