  Detailed Monte Carlo Inversion analysis of the spectral lines from three
Lyman limit systems (LLS) [N(HI) > 10^{17} cm^-2] and nine lower N(HI) systems
[2 10^{14} < N(HI) < 2 10^{16} cm^-2] observed in the VLT/UVES spectra of
Q0347-3819 (in the range 2.21 <= z <= 3.14) and of APM BR J0307-4945 (at z =
4.21 and 4.81) is presented. Combined with the results from a previous work,
the analyzed LLSs show that they are a heterogeneous population originating in
different environments. A functional dependence of the line-of-sight velocity
dispersion sigma_v on the absorber size L is confirmed: the majority of the
analyzed systems follow the scaling relation sigma_v ~ (N_H L)^{0.3} (with N_H
being the total gas column density). This means that most absorbers may be
related to virialized systems like galaxies or their halos. Previously noted
enhancement of the metal content in small size systems is also confirmed:
metallicities of Z ~ (1/3-1/2)Z_solar are found in systems with L < 0.4 kpc,
whereas we observe much lower metal abundances in systems with larger linear
sizes. For the first time in LLSs, a pronounced [alpha-element/iron-peak]
enrichment is revealed: the absorber at z = 2.21 shows [O/Fe] = 0.65+/-0.11,
[Si/Fe] = 0.51+/-0.11, and [Mg/Fe] = 0.38+/-0.11. Several absorption systems
exhibit characteristics which are very similar to that observed in
high-velocity clouds in the Milky Way and may be considered as high-redshift
counterparts of Galactic HVCs.
