2007A&A...470...67P

We present an analysis of the Lyman α forests of five quasar spectra in the near UV. Properties of the intergalactic medium (IGM) at an intermediate redshift interval (0.9≤z≤1.9) are studied. The amount of baryons in the diffuse photoionised IGM and the warm-hot intergalactic medium (WHIM) are traced to get constraints on the redshift evolution of the different phases of the intergalactic gas. The baryon density of the diffuse IGM is determined with photoionisation calculations under the assumption of local hydrostatic equilibrium. We assume that the gas is ionised by a metagalactic background radiation with a Haardt & Madau (2001, Clusters of Galaxies and the High Redshift Universe Observed in X-rays) spectrum. The WHIM is traced with broad Lyman α (BLA) absorption. The properties of a number of BLA detections are studied. Under the assumption of collisional ionisation equilibrium a lower limit to the baryon density could be estimated. It is found that the diffuse photoionised IGM contains at least ∼25% of the total baryonic matter at redshifts 1≲z≲2. For the WHIM a lower limit of ∼2.4% could be determined. Furthermore, the data indicates that the intergalactic gas is in a state of evolution at z∼1.5. We confirm that a considerable part of the WHIM is created between z=1 and z=2.