Letter to the Editor
A high-resolution study of the evolution of the
Lyman α forest in the redshift interval 
*
Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany e-mail: [ejanknecht,rbaade,dreimers]@hs.uni-hamburg.de
Corresponding author: E. Janknecht, ejanknecht@hs.uni-hamburg.de
Received:
15
April
2002
Accepted:
6
July
2002
Spectroscopy with HST/STIS Echelle and VLT/UVES
of the bright QSO HE 0515-4414 (
)
offers for the first time the opportunity to study the Lyman α forest
in the redshift range at a resolution ≤
10 km s-1.
The number density evolution of the Lyman α lines is well described
by the power law approach d
. We derive
for the strong lines
(
),
in agreement with the Lyman α forest evolution for 
.
The expected slow-down in their evolution does not appear
earlier than 
. For the weak lines
(
) we find
that the HE 0515-4414 data for 
follow the trend with 
known from observations, i.e. we confirm the difference in evolution
between weak and strong lines.
We use the two-point velocity correlation function (TPCF)
to search for clustering of the Lyman α lines,
yet we detect no excess in the TPCF on scales up to 10 000 km s-1.
Key words: cosmology: observations / intergalactic medium / quasars: Ly α forest / quasars: individual: HE 0515-4414
© ESO, 2002