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 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 [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 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 D n −σ relation.