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- Title
The evolution of H I and C IV quasar absorption line systems at 1.9 < z < 3.2.
- Authors
Kim, T.-S.; Partl, A. M.; Carswell, R. F.; Müller, V.
- Abstract
We have investigated the distribution and evolution of ~3100 intergalactic neutral hydrogen (HI) absorbers with H i column densities log NHI = [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 HI 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 HI absorbers at 1.9 < z < 3.2 into two samples, the unenriched forest and the CIV-enriched forest, depending on whether HI lines are associated with CIV at log NCIV ≥ 12.2 within a given velocity range. The entire HI column density distribution function (CDDF) can be described as the combination of these two well-characterised populations which overlap at log NHI ~ 15. At log NHI ≤ 15, the unenriched forest dominates, showing a similar power-law distribution to the entire forest. The CIV-enriched forest dominates at log NHI ≥ 15, with its distribution function as ∝NHI~-1.45. However, it starts to flatten out at lower NHI, since the enriched forest fraction decreases with decreasing NHI. The deviation from the power law at log NHI = [14,17] shown in the CDDF for the entire HI sample is a result of combining two different HI populations with a different CDDF shape. The total HI mass density relative to the critical density is ΩHI ~ 1.6 × 10-6 h-1, where the enriched forest accounts for ~40% of ΩHI.
- Subjects
HYDROGEN spectral lines; HYDROGEN absorption &; adsorption; SPECTRA of quasars; DISTRIBUTION (Probability theory); POWER law (Mathematics)
- Publication
Astronomy & Astrophysics / Astronomie et Astrophysique, 2013, Vol 552, Issue 2, pA77
- ISSN
0004-6361
- Publication type
Article
- DOI
10.1051/0004-6361/201220042