We explore the origin of the observed Ly \alpha and other UV lines from galaxies at z < 3.7 by detailed modelling of the spectra .
The objects are chosen among those showing a ) UV - optical - near-IR lines , b ) only UV lines and c ) those showing Ly \alpha in the UV and a few optical lines .
We also present UV line predictions for a sample of galaxies in the 0.0686 < z < 0.8829 range .
The sample of galaxies including Ly \alpha observations in their spectra does not show peculiar physical conditions of the emitting gas , nor abnormal element abundances .
However , the high velocity ( V _ { s } \geq 1000 km s ^ { -1 } ) component of the emitting gas is accompanied by relatively low preshock densities ( n _ { 0 } \sim 100-400 cm ^ { -3 } ) leading in some cases to broad forbidden lines .
Some spectra are best reproduced by shock dominated models in which the photoionizing source is hidden or absent .
Within more than 50 galaxies modelled in this work , only a few spectra from galaxies at z \geq 2.5 correspond to a starburst temperature T _ { * } > 10 ^ { 5 } K , similar to that found in galaxies showing some activity .