Volume 552, April 2013
|Number of page(s)||25|
|Section||Cosmology (including clusters of galaxies)|
|Published online||29 March 2013|
Leibniz-Institut für Astrophysik Potsdam,
An der Sternwarte 16,
2 Department of Astronomy, University of Wisconsin-Madison, 475 N. Charter St., Madison, WI 53706, USA
3 Institute of Astronomy, Madingley Road, Cambridge CB3 0HA, UK
Accepted: 10 February 2013
We have investigated the distribution and evolution of ~3100 intergalactic neutral hydrogen (H i) absorbers with H i column densities log NH i = [12.75,17.0] at 1.9 < z < 3.2, using 18 high resolution, high signal-to-noise quasar spectra obtained from the ESO VLT/UVES archive. We used two sets of Voigt profile fitting analysis, one including all the available high-order Lyman lines to obtain reliable H i column densities of saturated lines, and another using only the Lyα transition. There is no significant difference between the Lyα-only fit and the high-order Lyman fit results. Combining our Lyα-only fit results at 1.7 < z < 3.6 with high-quality literature data, the mean number density at 0 < z < 4 is not well described by a single power law and strongly suggests that its evolution slows down at z ≤ 1.5 at the high and low column density ranges. We also divided our entire H i absorbers at 1.9 < z < 3.2 into two samples, the unenriched forest and the C iv-enriched forest, depending on whether H i lines are associated with C iv at log NC iv ≥ 12.2 within a given velocity range. The entire H i column density distribution function (CDDF) can be described as the combination of these two well-characterised populations which overlap at log NH i ~ 15. At log NH i ≤ 15, the unenriched forest dominates, showing a similar power-law distribution to the entire forest. The C iv-enriched forest dominates at log NH i ≥ 15, with its distribution function as ∝NH i~−1.45. However, it starts to flatten out at lower NH i, since the enriched forest fraction decreases with decreasing NH i. The deviation from the power law at log NH i = [14,17] shown in the CDDF for the entire H i sample is a result of combining two different H i populations with a different CDDF shape. The total H i mass density relative to the critical density is ΩH i ~ 1.6 × 10-6 h-1, where the enriched forest accounts for ~40% of ΩH i.
Key words: quasars: absorption lines / cosmology: observations / large-scale structure of Universe
The data used in this study are taken from the ESO archive for the UVES at the VLT, ESO, Paranal, Chile.
Appendix A is available in electronic form at http://www.aanda.org
© ESO, 2013
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