  A significant fraction of the high-redshift galaxies show strong Lyman
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. Our aim is to analyse the Lyman alpha emission in a sample of
high-redshift UV-continuum selected galaxies and to derive the physical
conditions that determine the Lyman alpha profile and the line strength.
VLT/FORS spectra with a resolution of R ~ 2000 of 16 galaxies in the redshift
range of z = 2.7 to 5 are presented. The observed Lyman alpha profiles are
compared with theoretical models. The Lyman alpha lines range from pure
absorption (EW = -17 Angstroem) to strong emission (EW = 153 Angstroem). Most
Lyman 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 Msun uncorrected for dust absorption. The Lyman
alpha emission strength of our target galaxies is found to be determined by the
amount of dust and the kinematics of the outflowing material.
