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Astron. Astrophys. 361, 803-810 (2000)

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UVES observations of QSO 0000-2620: molecular hydrogen abundance in the damped Ly[FORMULA] system at zabs = 3.3901 *

S.A. Levshakov 1, P. Molaro 2, M. Centurión 2, S. D'Odorico 3, P. Bonifacio 2 and G. Vladilo 2

1 Department of Theoretical Astrophysics, Ioffe Physico-Technical Institute, 194021 St. Petersburg, Russia
2 Osservatorio Astronomico di Trieste, Via G.B. Tiepolo 11, 34131 Trieste, Italy
3 European Southern Observatory, 85748 Garching bei München, Germany

Received 24 May 2000 / Accepted 19 July 2000


We have discovered molecular hydrogen in a fourth quasar damped Ly[FORMULA] system (hereafter DLA). The UVES spectrograph on the 8.2m ESO Kueyen telescope has allowed the detection of H2 in gas with low metallicity, [FORMULA], and high neutral hydrogen column density, [FORMULA] cm-2, at redshift [FORMULA] toward QSO 0000-2620. The measured H2 fractional abundance of [FORMULA] is lower than a typical value for Galactic interstellar clouds of high [FORMULA] column density by a factor of [FORMULA]. Since H2 molecules are formed efficiently on dust grains, it implies that the dust condensation in this DLA is negligible, and hence the abundances derived from metal absorption lines are the actual ones. The obtained [FORMULA] value leads to an estimate of the dust number density of [FORMULA], which is consistent with the dust-to-gas ratio [FORMULA] derived independently from the [Cr/Zn] and [Fe/Zn] ratios.

Key words: ISM: molecules – line: profiles – galaxies: quasars: absorption lines – galaxies: quasars: individual: Q0000 – 2620

* Based on public data released from the UVES commissioning at the VLT Kueyen telescope, European Southern Observatory, Paranal, Chile.

Send offprint requests to: S.A. Levshakov (lev@astro.ioffe.rssi.ru)

© European Southern Observatory (ESO) 2000

Online publication: October 2, 2000