3 research outputs found
Large scale environmental bias of the QSO line of sight proximity effect
We analyse the proximity zone of the intergalactic matter around
high-redshift quasars in a cosmological environment. In a box of 64 h-1 Mpc
base length we employ dark matter only simulations. For estimating the hydrogen
temperature and density distribution we use the effective equation of state.
Hydrogen is assumed to be in photoionisation equilibrium with a model
background flux which is fit to recent observations of the mean optical depth
and transmission flux statistics. At redshifts z = 3, 4, and 4.8, we select
model quasar positions at the centre of the 20 most massive halos and 100 less
massive halos identified in the simulation. From each assumed quasar position
we cast 100 random lines of sight for two box length including the changes in
the ionisation fractions by the QSO flux field and derive mock Ly{\alpha}
spectra. The proximity effect describes the dependence of the mean normalised
optical depth {\xi} = {\tau}eff, QSO/{\tau}eff, Ly{\alpha} as a function of the
ratio of the ionisation rate by the QSO and the background field, {\omega} =
{\Gamma}QSO/{\Gamma}UVB, i.e. the profile {\xi} = (1 + {\omega}/a)-0.5, where a
strength parameter a is introduced. The strength parameter measures the
deviation from the theoretical background model and is used to quantify any
influence of the environmental density field. We reproduce an unbiased
measurement of the proximity effect which is not affected by the host halo
mass. The scatter between different lines of sight and different quasar host
positions increases with decreasing redshift. Around the host halos, we find
only a slight average overdensity in the proximity zone at comoving radii of 1
< rc < 10h-1 Mpc. However, a clear power-law correlation of the strength
parameter with the average overdensity in rc is found, showing an
overestimation of the ionising background in overdense regions and an
underestimation in underdense regions.Comment: Accepted by Monthly Notices of the Royal Astronomical Society. 15
pages, 12 figure
The evolution of HI and CIV quasar absorption line systems at 1.9 < z < 3.2
We have investigated the distribution and evolution of ~3100 intergalactic HI
absorbers with HI column densities log N(HI) = [12.75, 17.0] at 1.9 < z < 3.2,
using 18 high resolution, high S/N 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 Ly-alpha lines. There
is no significant difference between the results from the two fits. Combining
our results with 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 N(CIV) > 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
N(HI) ~ 15. At log N(HI) < 15, the unenriched forest dominates, showing a
similar power-law distribution to the entire forest. The CIV-enriched forest
dominates at log N(HI) > 15, with its distribution function proportional to
N(HI)^(-1.45). However, it starts to flatten out at lower N(HI), since the
enriched forest fraction decreases with decreasing N(HI). The deviation from
the power law at log N(HI) = [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
Omega(HI) ~ 1.6 x 10^(-6) h^(-1), where the enriched forest accounts for ~40%
of Omega(HI).Comment: 26 pages, 20 figures, accepted for AA, in pres