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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. ReimersHamburger 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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