| Abstract
| - We present optical and near-infrared spectroscopic observations of the optical Einstein ring 0047 - 2808. We detect both [O III] lines λλ4959, 5007 near ∼ 2.3 μm, confirming the redshift of the lensed source as z = 3.595. The Lyα line is redshifted relative to the [OIII] line by 140 ± 20 km s−1. Similar velocity shifts have been seen in nearby starburst galaxies. The [OIII] 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 σ = 55 km s−1 is considerably smaller than the value predicted by Baugh et al. for the somewhat brighter Lyman-break galaxies. The Lyα 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 Dn−σ relation.
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