EDP Sciences
Free access
Issue A&A
Volume 456, Number 3, September IV 2006
Page(s) L9 - L12
Section Letters
DOI http://dx.doi.org/10.1051/0004-6361:20065769

A&A 456, L9-L12 (2006)
DOI: 10.1051/0004-6361:20065769


Metallicity as a criterion to select H $\mathsf{_2}$-bearing damped Lyman- $\mathsf{\alpha}$ systems

P. Petitjean1, 2, C. Ledoux3, P. Noterdaeme3 and R. Srianand4

1  Institut d'Astrophysique de Paris, CNRS - Université Pierre et Marie Curie, 98bis boulevard Arago, 75014 Paris, France
    e-mail: petitjean@iap.fr
2  LERMA, Observatoire de Paris, 61 avenue de l'Observatoire, 75014 Paris, France
3  European Southern Observatory, Alonso de Córdova 3107, Casilla 19001, Vitacura, Santiago, Chile
4  IUCAA, Post Bag 4, Ganesh Khind, Pune 411 007, India

(Received 7 June 2006 / Accepted 16 July 2006)

Aims.We characterize the importance of metallicity on the presence of molecular hydrogen in damped Lyman-$\alpha$ (DLA) systems.
Methods.We constructed a representative sample of 18 DLA/sub-DLA systems with log N(H I) > 19.5 at high redshift ( $z_{\rm abs}$ > 1.8) and with metallicities relative to solar [X/H] > -1.3 (with [X/H] = log N(X)/N(H)-log (X/H)$_{\odot}$ and X either Zn, S or Si). We gathered data covering the expected wavelength range of redshifted H2 absorption lines on all systems in the sample from either the literature (10 DLAs), the UVES-archive, or new VLT-UVES observations for four of them. The sample is large enough to allow us to discuss for the first time the importance of metallicity as a criterion for the presence of molecular hydrogen in the neutral phase at high-z.
Results.From the new observations, we report two new detections of molecular hydrogen in the systems at $z_{\rm abs} = 2.431$ toward Q 2343+125 and at $z_{\rm abs}= 2.426$ toward Q 2348-011. Q 2348-011, From a comparison of the H2 detection fraction in the high-metallicity sample with earlier results, we find that the fraction of DLA systems with log f = log 2N(H2)/(2N(H2) + N(H I)) > -4 is as large as 50% for [X/H] > -0.7, when it is only ~5% for [X/H] < -1.3 and ~15% in the overall sample (with -2.5 < [X/H] < -0.3). This demonstrates that the presence of molecular hydrogen at high redshift is strongly correlated with metallicity.

Key words: galaxies: high-redshift -- galaxies quasars: absorption lines -- galaxies quasars: individual: Q 2343+125 -- galaxies quasars: individual: Q 2348-011

© ESO 2006

What is OpenURL?

The OpenURL standard is a protocol for transmission of metadata describing the resource that you wish to access. An OpenURL link contains article metadata and directs it to the OpenURL server of your choice. The OpenURL server can provide access to the resource and also offer complementary services (specific search engine, export of references...). The OpenURL link can be generated by different means.
  • If your librarian has set up your subscription with an OpenURL resolver, OpenURL links appear automatically on the abstract pages.
  • You can define your own OpenURL resolver with your EDPS Account. In this case your choice will be given priority over that of your library.
  • You can use an add-on for your browser (Firefox or I.E.) to display OpenURL links on a page (see http://www.openly.com/openurlref/). You should disable this module if you wish to use the OpenURL server that you or your library have defined.

Editor-in-Chief: T. Forveille
Letters Editor-in-Chief: J. Alves
Managing Editor: C. Bertout

ISSN: 0004-6361 ; e-ISSN: 1432-0746
Frequency: 12 volumes per year
Published by: EDP Sciences

Mirror sites: CDS | EDP Sciences
  RSS feeds
© The European Southern Observatory (ESO)