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The Aim of our study is to understand the variety of observed Lyman-alpha(Lya) line profiles and strengths in Lyman Break Galaxies (LBGs) and Lyaemitters (LAEs), the physical parameters governing them, and hence derivingconstraints on the gas and dust content and stellar populations of theseobjects.  Using our 3D Lya radiation transfer code including gas and dust (Verhamme etal. 2006), we fit 11 LBGs from the FORS Deep Field with redshifts between 2.8and 5 observed by Tapken et al. (2007). A simple geometry of a sphericallyexpanding shell of HI is adopted.  RESULTS : The variety of observed Lya profiles is successfully reproduced.Most objects show outflow velocities of 150-200 km/s; two objects are mostlikely quasi-static. The radial HI column density ranges from NH=2.10^{19} to7.10^{20} cm^{-2}. Our Lya profile fits yield values of E(B-V)~0.05-0.2 for thegas extinction. We find indications for a dust-to-gas ratio higher than theGalactic value, and for a substantial scatter. The escape fraction of Lyaphotons is found to be determined primarily by the extinction, and a simple fitformula is proposed. Intrinsic EW(Lya)~50-100 Angstroms are found for 8/11objects, as expected for stellar populations forming constantly over longperiods (> 10-100 Myr). In three cases we found indications for youngerpopulations. Correlations between the observed EW(Lya) and other observablessuch as FWHM(Lya), E(B-V),SFR(UV) etc, are reproduced. We also show that thereis a clear overlap between LBGs and LAEs. Radiation transfer and dust effectsexplain the increase of the LAE/LBG ratio, and a higher percentage of LBGs withstrong Lya emission with increasing redshift. [shortened]

astronomy and astrophysics

3D Lyman-alpha radiation transfer. III. Constraints on gas and stellar  properties of z~3 Lyman break galaxies (LBG) and implications for high-z LBGs  and Lyman-alpha emitters(LAEs)