A high-resolution study of the evolution of the Lyman α forest in the redshift interval $0.9 < z < 1.7$

Abstract

Spectroscopy with HST/STIS Echelle and VLT/UVES of the bright QSO HE 0515 4414 (zem= 1:73; B= 15:0) oers for the first time the opportunity to study the Lyman forest in the redshift range 0:9 1:7. The expected slow-down in their evolution does not appear earlier than z 1. For the weak lines (13:10 logNHi 14:00) we find that the HE 0515 4414 data for z> 1 follow the trend with= 1:40 known from z> 1:7 observations, i.e. we confirm the dierence in evolution between weak and strong lines. We use the two-point velocity correlation function (TPCF) to search for clustering of the Lyman lines, yet we detect no excess in the TPCF on scales up to 10 000 km s 1 .