We present UVES observations of the log N ( H i )  = 21.7 damped Lyman- \alpha system at z _ { abs }  = 2.03954 towards the quasar PKS 0458 - 020 .
H i Lyman- \alpha emission is detected in the center of the damped Lyman- \alpha absorption trough .
Metallicities are derived for Mg ii , Si ii , P ii , Cr ii , Mn ii , Fe ii and Zn ii and are found to be -1.21 \pm 0.12 , -1.28 \pm 0.20 , -1.54 \pm 0.11 , -1.66 \pm 0.10 , -2.05 \pm 0.11 , -1.87 \pm 0.11 , -1.22 \pm 0.10 , respectively , relative to solar .
The depletion factor is therefore of the order of [ Zn/Fe ] = 0.65 .
We observe metal absorption lines to be blueshifted compared to the Lyman- \alpha emission up to a maximum of \sim 100 and 200 km s ^ { -1 } for low and high-ionization species respectively .
This can be interpreted either as the consequence of rotation in a large ( \sim 7Â kpc ) disk or as the imprint of a galactic wind .
The star formation rate ( SFR ) derived from the Lyman- \alpha emission , 1.6Â M _ { \odot } yr ^ { -1 } , is compared with that estimated from the observed CÂ ii ^ { * } absorption .
No molecular hydrogen is detected in our data , yielding a molecular fraction \mathrm { log } f < -6.52 .
This absence of H _ { 2 } can be explained as the consequence of a high ambient UV flux which is one order of magnitude larger than the radiation field in the ISM of our Galaxy and originates in the observed emitting region .