The number density and clustering properties of Lyman-break galaxies ( LBGs ) are consistent with them being the central galaxies of the most massive dark halos present at z \sim 3 .
This conclusion holds in all currently popular hierarchical models for structure formation , and is almost independent of the global cosmological parameters .
We examine whether the sizes , luminosities , kinematics and star-formation rates of LBGs are also consistent with this identification .
Simple formation models tuned to give good fits to low redshift galaxies can predict the distribution of these quantities in the LBG population .
The LBGs should be small ( with typical half-light radii of 0.6 - 2 { h ^ { -1 } { kpc } } ) , should inhabit haloes of moderately high circular velocity ( 180 - 290 { { km s ^ { -1 } } } ) but have low stellar velocity dispersions ( 70 - 120 { { km s ^ { -1 } } } ) and should have substantial star formation rates ( 15 - 100 M _ { \odot } yr ^ { -1 } ) .
The numbers here refer to the predicted median values in the LBG sample of Adelberger et al .
( 1998 ) ; the first assumes an \Omega _ { 0 } = 1 universe and the second a flat universe with \Omega _ { 0 } = 0.3 .
For either cosmology these predictions are consistent with the current ( rather limited ) observational data .
Following the work of Kennicutt ( 1998 ) we assume stars to form more rapidly in gas of higher surface density .
This predicts that LBG samples should preferentially contain objects with low angular momentum , and so small size , for their mass .
In contrast , samples of damped Ly \alpha systems ( DLSs ) , should be biased towards objects with large angular momentum .
Bright LBGs and DLSs may therefore form distinct populations , with very different sizes and star formation rates , LBGs being smaller and more metal-rich than DLSs of similar mass and redshift .