The physical properties of the Lyα forest at

Abstract

Combining a new, increased data set of eight quasi‐stellar objects (QSOs) covering the Lyα forest at redshifts 1.5 < z < 3.6 from VLT/UVES observations with previously published results, we have investigated the properties of the Lyα forest at 1.5 < z <4. With the six QSOs covering the Lyα 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 Lyα forest at z≤ 2.5, where the Lyα forest starts to show some inhomogeneity from sightline to sightline. We have fitted Voigt profiles to the Lyα absorption lines as in previous studies, and have, for two QSOs with zem∼ 2.4, fitted Lyα and higher order of Lyman lines down to 3050 Å simultaneously. This latter approach has been taken in order to study the Lyβ forest at z∼ 2.2 and the higher H i column density Lyα forest in the Lyβ forest region. For a given NH I range, the Lyα forest at 1.5 < z < 4 shows the monotonic evolution, which is governed mainly by the Hubble expansion at this redshift range. In general, the Lyα forest line number density (dn/dz) is best approximated with dn/dz= 6.1(1 +z)2.47 ± 0.18 for the H i column density NH I= 1013.64−17 cm−2 at 1.5 < z < 4. When the results at 0 < z < 1.5 from Hubble Space Telescope (HST) observations are combined, the slow‐down in the number density evolution occurs at z < 1.5. For higher column density clouds at NH i > 1014 cm−2, there is a variation in the line number density from sightline to sightline at z < 2.5. This variation is stronger for higher column density systems, probably due to more gravitationally evolved structures at lower z. The mean H i opacity is at 1.5 < z < 4. HST observations show evidence for slower evolution of at z < 1. For NH i= 1012.5–15 cm−2, the differential column density distribution function, f(NH i), can be best fitted by f(NH I∝NH i−β with β≈ 1.5 for 1.5 < z < 4. When combined with HST observations, the exponent β increases as z decreases at 0 < z < 4 for NH i= 1013–17 cm−2. The correlation strength of the step optical depth correlation function shows the strong evolution from 〈z〉= 3.3 to 〈z〉= 2.1, although there is a large scatter along different sightlines. The analyses of the Lyβ forest at z∼ 2.2 are, in general, in good agreement with those of the Lyα forest.

The evolution of H i and C iv quasar absorption line systems at 1.9 <z< 3.2

“…The result from the HST/FOS Quasar Absorption Line Key project shows such a slow change in the dn/dz evolution at z < 1.5 (Weymann et al 1998), compared to a much steeper dn/dz evolution shown at z > 2 ( Kim et al 1997Kim et al , 2001Kim et al , 2002. Cosmic variance also seems to increase at lower z .…”

“…Note that the redshift based on the emission lines is known to be underestimated compared to the one measured from other quasar emission lines such as C iv (Tytler & Fan 1992;Vanden Berk et al 2001). The spectrum of Q1101−264 is the same one as analysed in Kim et al (2002), while the rest of spectra are from Kim et al (2007). The raw spectra were obtained from the ESO VLT/UVES archive and were reduced with the UVES pipeline.…”

The Enrichment History of the Intergalactic Medium: Oviin Lyα Forest Systems at Redshiftz ∼ 2

“…Some spectral regions and results for HE 1122À1648 are described by Kim et al (2002). The spectral range covered by the analysis is from 3050 Å to the C iv emission line in both cases.…”

“…The continuum was initially determined as described by Kim et al (2002), and the absorption lines were fitted by multiple Voigt profiles, using the VPFIT program described by Webb (1987;Rauch et al 1992) as updated by R. F. Carswell et al 5 The whole of the available spectrum was fitted so as to provide a self-consistent set of line profile parameters for each ion. Except where noted otherwise below, different ions with components in the same system were not constrained to have the same redshift, and their Doppler parameters were fitted independently.…”

The Contribution of UVES@VLT to the New Era of QSO Absorption Line Studies

“…The statistical and physical properties of Ly-α (e.g. [13,21]) and C IV (e.g. [22]) absorbers were refined and assessed.…”