We present an intermediate resolution , high S/N spectrum of the z = 2.7268 galaxy MS 1512 - cB58 , obtained with LRIS on the Keck I telescope and covering the rest frame far-UV from 1150 to 1930 Å. Gravitational lensing by a foreground cluster boosts the flux from cB58 by a factor of \sim 30 and provides the opportunity for a first quantitative study of the physical properties of star forming galaxies at high redshift .
The spectrum we have recorded is very rich in stellar and interstellar features ; from their analysis we deduce the following main results .

The ultraviolet spectral properties of cB58 are remarkably similar to those of nearby star forming galaxies and spectral synthesis models based on libraries of O and B stars can reproduce accurately the fine detail of the integrated stellar spectrum .
The P-Cygni profiles of C IV and N V are best matched by continuous star formation with a Salpeter IMF extending beyond M = 50 ~ { } M _ { \odot } —we find no evidence for either a flatter IMF ( at the high mass end ) , or an IMF deficient in the most massive stars .
There are clues in our data that the metallicity of both the stars and the gas is a few times below solar .
Our best estimate , Z _ { cB 58 } \approx 1 / 4 ~ { } Z _ { \odot } , is \approx 3 times higher than the typical metallicity of damped Lyman \alpha systems at the same redshift , consistent with the proposal that the galaxies which dominate the H I absorption cross-section are generally forming stars at a slower rate than L ^ { * } Lyman break galaxies like cB58 .
The relative velocities of the stellar lines , interstellar absorption , and H II emission indicate the existence of large-scale outflows in the interstellar medium of cB58 , with a bulk outward motion of 200 km s ^ { -1 } and a mass loss rate of \approx 60 ~ { } M _ { \odot } yr ^ { -1 } , roughly comparable to the star formation rate .
Such galactic winds seem to be a common feature of starburst galaxies at all redshifts , and may well be the mechanism which self-regulates star formation , distributes metals over large volumes and allows the escape of ionizing photons into the IGM .

We suggest further observations of cB58 which should provide more precise measurements of element abundances and of detailed physical parameters , and highlight the need to identify other examples of gravitationally lensed galaxies for a comprehensive study of star formation at early times .