Context : A significant fraction of the high-redshift galaxies show strong { Ly } { \alpha } emission lines .
For redshifts z > 5 , most known galaxies belong to this class .
However , so far not much is known about the physical structure and nature of these objects .

Aims : Our aim is to analyse the { Ly } { \alpha } emission in a sample of high-redshift UV-continuum selected galaxies and to derive the physical conditions that determine the { Ly } { \alpha } profile and the line strength .

Methods : VLT/FORS spectra with a resolution of R \approx 2000 of 16 galaxies in the redshift range of z = 2.7 to 5 are presented .
The observed { Ly } { \alpha } profiles are compared with theoretical models .

Results : The { Ly } { \alpha } lines range from pure absorption ( EW = -17 Å ) to strong emission ( EW = 153 Å ) .
Most { Ly } { \alpha } emission lines show an asymmetric profile , and three galaxies have a double-peaked profile .
Both types of profiles can be explained by a uniform model consisting of an expanding shell of neutral and ionised hydrogen around a compact starburst region .
The broad , blueshifted , low-ionisation interstellar absorption lines indicate a galaxy-scale outflow of the ISM .
The strengths of these lines are found to be determined in part by the velocity dispersion of the outflowing medium .
We find star-formation rates of these galaxies ranging from SFR _ { UV } = 1.2 to 63.2 { M } _ { \odot } yr ^ { -1 } uncorrected for dust absorption .

Conclusions : The { Ly } { \alpha } emission strength of our target galaxies is found to be determined by the amount of dust and the kinematics of the outflowing material .