QSO Absorption Lines as a Cosmological Probe: Exploring the Lyman Forest with VLT/UVES

Abstract.

The remarkable efficiency of the Ultra-Violet Echelle Spectrograph (UVES) at the VLT has made it possible to push high-resolution, high-S/N ground observations of the Ly$\alpha$ forest down to $z \sim 1.5$, gaining new insight into the physical state of the intergalactic medium (IGM) and its evolution over more than 90% of the cosmic time. The results presented here are based on recent UVES observations of the spectra of 8 QSOs, covering the Ly$\alpha$ forest at $1.5 < z_{Ly\alpha} < 3.6$ with S/N $\sim 40-50$ and resolution $R \sim 45000$ [1,2]. The absorption lines were fit to the Voigt profiles to derive the three line parameters: absorption redshift, z, the HI column density, N _HI in cm^-2, and the Doppler parameters, b in km s^-1.