EDP Sciences
Free Access
Volume 415, Number 3, March I 2004
Page(s) 879 - 884
Section Extragalactic astronomy
DOI https://doi.org/10.1051/0004-6361:20034584

A&A 415, 879-884 (2004)
DOI: 10.1051/0004-6361:20034584

Hints of star formation at z $\mathsf{>6}$: The chemical abundances of the DLA system in the QSO BRI 1202-0725 (z $\mathsf{_{abs}=4.383}$)

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- $\alpha$ (DLA) absorber at redshift $z_{\rm abs}=4.383$ observed toward QSO BRI 1202-0725 is studied by means of high resolution (FWHM  $\approx 7$ 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]  $=0.08\pm
0.13$ and [Si/C]  $=0.31\pm0.07$. [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 $z_{\rm abs} = 4.466$. The current interpretation of the bimodal distribution of N abundances in DLAs implies that large [ N/ $\alpha$]  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, dodorico@sissa.it

SIMBAD Objects

© ESO 2004

Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.

Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.

Initial download of the metrics may take a while.