A&A 415, 879-884 (2004)
Hints of star formation at z : The chemical abundances of the DLA system in the QSO BRI 1202-0725 (z )V. D'Odorico and P. Molaro
INAF - Osservatorio Astronomico di Trieste, via G.B. Tiepolo, 11, 34131 Trieste, Italy
(Received 23 July 2003 / Accepted 30 October 2003 )
The Damped Ly- (DLA) absorber at redshift observed toward QSO BRI 1202-0725 is studied by means of high resolution (FWHM km s -1) 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] and [Si/C] . [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 . The current interpretation of the bimodal distribution of N abundances in DLAs implies that large [ N/ ] values correspond to relatively old systems. Adopting a scale time of 500 Myrs for full N production by intermediate mass stars, the onset of star formation in our DLA took place already at redshift > 6.
Key words: galaxies: abundances -- galaxies: high-redshift -- galaxies: quasars: absorption lines -- cosmology: observations
Offprint request: V. D'Odorico, firstname.lastname@example.org
© ESO 2004