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A&A 386, 796-800 (2002)
DOI: 10.1051/0004-6361:20020342

Fine-structure diagnostics of neutral carbon toward  HE 0515-4414

R. Quast, R. Baade and D. Reimers

Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany
    e-mail: [rbaade,dreimers]@hs.uni-hamburg.de

(Received 30 November 2001 / Accepted 5 March 2002)

Abstract
New high-resolution high signal-to-noise spectra of the z=1.15 damped Lyman  (DLA) system toward the quasi-stellar object HE 0515-4414 reveal absorption lines of the multiplets 2 and 3 in . The resonance lines are seen in two components with total column densities of and , respectively. The comparision of theoretical calculations of the relative fine-structure population with the ratios of the observed column densities suggests that the absorbing medium is either very dense or exposed to very intense UV radiation. The upper limit on the local UV energy density is 100 times the galactic UV energy density, while the upper limit on the number density is 110 cm ^-3. The excitation temperatures of the ground state fine-structure levels of T=15.7 and T=11.1 K, respectively, are consistent with the temperature-redshift relation predicted by the standard Friedmann cosmology. The cosmic microwave background radiation (CMBR) is only a minor source of the observed fine-structure excitation.

Key words: cosmic microwave background -- intergalactic medium -- quasars: absorption lines -- quasars: individual: HE 0515-4414

Offprint request: R. Quast, rquast@hs.uni-hamburg.de

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