Fulltext

A homogeneous sample of sub-damped Lyman α systems — I. Construction of the sample and chemical abundance measurements

Dessauges-Zavadsky, M. ; Péroux, C. ; Kim, T.-S ; D'Odorico, S. ; McMahon, R. G.

In: Monthly Notices of the Royal Astronomical Society, 2003, vol. 345, no. 2, p. 447-479

Aggiungi alla tua lista
    Titre
    • A homogeneous sample of sub-damped Lyman α systems — I. Construction of the sample and chemical abundance measurements
    Auteur
    • Dessauges-Zavadsky, M.. Observatoire de Genève, 1290 Sauverny, Switzerland
    • Péroux, C.. Osservatorio Astronomico di Trieste, Via G. B. Tiepolo 11, 34131 Trieste, Italy
    • Kim, T.-S. European Southern Observatory, Karl-Schwarzchild-Str. 2, 85748 Garching bei München, Germany
    • D'Odorico, S.. European Southern Observatory, Karl-Schwarzchild-Str. 2, 85748 Garching bei München, Germany
    • McMahon, R. G.. Institute of Astronomy, Madingley Road, Cambridge CB3 0HA
    Type de document
    • Postprint
    Langue
    • Inglese
    Publié dans
    • Monthly Notices of the Royal Astronomical Society, 2003, vol. 345, no. 2, p. 447-479. Blackwell Science Ltd
    Autre version électronique
    Identifiant OAI-PMH
    • oai:doc.rero.ch:298225
    Summary
    In this first paper of a series, we report on the use of quasar spectra obtained with the high-resolution Ultraviolet-Visual Echelle Spectrograph (UVES) and available through the European Southern Observatory (ESO) Very Large Telescope (VLT) archive to build the first homogeneous and unbiased sample of sub-damped Lyman α (sub-DLA) systems, absorbers with Hi column densities >1019 cm−2 but lower than the classical definition of damped Lyman α systems (2 × 1020 cm−2). A systematic investigation of the properties of these systems and a comparison with those of the DLAs (Paper II of this series) is expected to provide new clues on the association of high column density absorbers with galaxies and on the overall evolution of the neutral hydrogen gas mass and metal content in the Universe. In the spectra of 22 quasars which were found suitable for a sub-DLA search, we identified 12 sub-DLAs and one borderline case between the DLA and sub-DLA systems in the redshift interval z= 1.8-4.3. We measured the column densities of Hi and of up to 16 additional ions of low, intermediate and high ionization: Oi, Cii, Civ, Siii, Siiv, Ni, Sii, Mgi, Mgii, Alii, Aliii, Feii, Feiii, Niii, Znii and Crii. We further investigated the significance of the ionization corrections in the determination of the chemical abundances from the low-ionization ions in the sub-DLA Hi column density range. Using the predictions of different ion ratios as a function of the ionization parameter computed using the cloudy software package, we have estimated that with the exception of one case, the ionization corrections to the abundances of nine systems for which we were able to constrain the ionization parameter are lower than 0.2 dex for all of the elements except Alii and Znii down to Hi column densities of logN(Hi)=19.3 cm−2. Finally, we present the first sub-DLA chemical abundance data base, which contains the abundance measurements of 11 different elements (O, C, Si, N, S, Mg, Al, Fe, Ni, Zn and Cr). We took advantage of the lower Hi column densities in sub-DLAs to measure, in particular, the O and C abundances using lines that are normally saturated in DLAs