2004A&A...415..879D

The Damped Ly-α (DLA) absorber at redshift z_abs=4.383 observed toward QSO BRI 1202-0725 is studied by means of high resolution (FWHM≃7km/s) VLT-UVES spectra. We refine a previously determined Si abundance and derive with confidence abundances for C, N and O which are poorly known in DLAs. The [O/Fe] ratio is ∼0.6, but we cannot establish if iron is partially locked into dust grains. The [C/Fe]=0.08±0.13 and [Si/C]=0.31±0.07. [N/O] and [N/Si] are about -1, which is consistent with the majority of DLAs. This value is much larger than the one observed for the DLA toward QSO J 0307-4945 at z_abs=4.466. The current interpretation of the bimodal distribution of N abundances in DLAs implies that large [N/α] values correspond to relatively old systems. Adopting a scale time of 500Myrs for full N production by intermediate mass stars, the onset of star formation in our DLA took place already at redshift >6.