Volume 480, Number 2, March III 2008
|Page(s)||349 - 357|
|Published online||09 January 2008|
The nitrogen and oxygen abundances in the neutral gas at high redshift*
Institut d'Astrophysique de Paris, CNRS and UPMC Paris 6, UMR7095, 98bis boulevard Arago, 75014 Paris, France e-mail: email@example.com
2 European Southern Observatory, Alonso de Córdova 3107, Casilla 19001, Vitacura, Santiago, Chile
3 IUCAA, Post Bag 4, Ganesh Khind, Pune 411 007, India
Accepted: 18 December 2007
Aims.We study the oxygen and nitrogen abundances in the interstellar medium of high-redshift galaxies.
Methods.We use high resolution and high signal-to-noise ratio spectra of damped Lyman-α (DLA) systems detected along the line-of-sight to quasars to derive robust abundance measurements from unsaturated metal absorption lines.
Results.We present results for a sample of 16 high-redshift DLAs and strong sub-DLAs (log N(H I) > 19.5, 2.4 < zabs < 3.6) including 13 new measurements. We find that the oxygen to iron abundance ratio is pretty much constant with [O/Fe] ~ +0.32±0.10 for -2.5 < [O/H] < -1.0 with a small scatter around this value. The oxygen abundance follows quite well the silicon abundance within ~0.2 dex, although the silicon abundance could be slightly smaller for [O/H] < -2. The distribution of the [N/O] abundance ratio, measured from components that are detected in both species, is somehow double peaked: five systems have [N/O] > -1 and nine systems have [N/O] < -1.15. In the diagram [N/O] versus [O/H], a loose plateau is possibly present at [N/O] ~ -0.9, which is below the so-called primary plateau as seen in local metal-poor dwarf galaxies ([N/O] in the range -0.57 to -0.74). No system is seen above this primary plateau whereas the majority of the systems lie well below with a large scatter. All this suggests a picture in which DLAs undergo successive star-bursts. During such an episode, the [N/O] ratio decreases sharply because of the rapid release of oxygen by massive stars, whereas inbetween two bursts, nitrogen is released by low and intermediate-mass stars with a delay and the [N/O] ratio increases.
Key words: ISM: abundances / Galaxy: abundances / galaxies: quasars: absorption lines
Based on observations carried out at the European Southern Observatory (ESO), under visitor mode progs. ID 65.O-0063, 66.A-0624, 67.A-0078 and 68.A-0600 with the UVES echelle spectrograph installed at the ESO Very Large Telescope (VLT), unit Kueyen, on mount Paranal in Chile. Also based on archival data from progs. 68.A-0492 (PI: D'Odorico), 68.B-0115 (PI: Molaro) and 69.A-0051 (PI: Pettini).
© ESO, 2008
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.