Issue |
A&A
Volume 374, Number 3, August II 2001
|
|
---|---|---|
Page(s) | 871 - 877 | |
Section | Cosmology (including clusters of galaxies) | |
DOI | https://doi.org/10.1051/0004-6361:20010777 | |
Published online | 15 August 2001 |
High-resolution OVI absorption line observations at
1.2
1.7 in the bright QSO HE 0515-4414*
1
Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany e-mail: rbaade@hs.uni-hamburg.de, hhagen@hs.uni-hamburg.de
2
Departamento de Astronomia, Universidad de Chile, Casilla 36-D, Santiago, Chile e-mail: slopez@rhea.das.uchile.cl
Corresponding author: D. Reimers, dreimers@hs.uni-hamburg.de
Received:
7
March
2001
Accepted:
25
May
2001
STIS Echelle observations at a resolution of and UVES/VLT spectroscopy at a resolution of
of the luminous QSO HE 0515-4414 (
,
) reveal four intervening Ovi absorption
systems in the redshift range
(1.38503, 1.41601, 1.60175, 1.67359). In addition, two associated
systems at
and
are present. Noteworthy
is an absorber at
with
and strong Ovi (N(Ovi)/N(Hi)
≈ 1) and Civ doublets, while a nearby much
stronger Ly α absorber (log
,
) does not reveal any heavy element
absorption. For the first time, high resolution observations allow one
to measure radial velocities of Hi, Civ and
Ovi simultaneously in several absorption systems (1.385,
1.674, 1.697) with the result that significant velocity
differences (up to
, are observed between
Hi and Ovi, while smaller differences (up to
) are seen between Civ and
Ovi. We tentatively conclude that Hi, Ovi,
and Civ are not formed in the same volumes and that
therefore conclusions on ionization mechanisms are not possible
from the observed column density ratios Ovi/Hi or
Ovi/Civ. The number density of Ovi
absorbers with
mÅis
, roughly a factor of 5 less than that found by
Tripp et al. ([CITE]) at low redshift. However, this number is
uncertain and further lines of sight will be probed in the next
HST cycle. An estimate of the cosmological mass-density of the
Ovi-phase yields
for
and an assumed
ionization fraction Ovi/O = 0.2. It should be noted that
this result is subject to large systematic errors. This
corresponds to an increase by roughly a factor of 15 between
(this work) and the value found by Tripp et al.
([CITE]) at
, if the same oxygen abundance
is assumed. Agreement with the simulations by Davé
et al. ([CITE]) can be obtained, if the oxygen abundance increases
by a factor of ~3 over the same redshift interval.
Key words: cosmology: observations / intergalactic medium / quasars: absorption lines / quasars: individual: HE 0515-4414
© ESO, 2001
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