Description
Combining a new, increased data set of eight quasi-stellar objects (QSOs) covering the Ly{alpha} forest at redshifts 1.5<z<3.6 from VLT/UVES observations with previously published results, we have investigated the properties of the Ly{alpha} forest at 1.5<z<4. With the six QSOs covering the Ly{alpha} forest at 1.5<z<2.5, we have extended previous studies in this redshift range. In particular, we have concentrated on the evolution of the line number density and the clustering of the Ly{alpha} forest at z<=2.5, where the Ly{alpha} forest starts to show some inhomogeneity from sightline to sightline. We have fitted Voigt profiles to the Ly{alpha} absorption lines as in previous studies, and have, for two QSOs with z_em_~2.4, fitted Ly{alpha} and higher order of Lyman lines down to 3050{AA} simultaneously. This latter approach has been taken in order to study the Ly{beta} forest at z~2.2 and the higher H I column density Ly{alpha} forest in the Ly{beta} forest region.
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