2003ApJ...582..596L

Detailed Monte Carlo inversion analysis of the spectral lines from three Lyman limit systems (LLSs) [N(HI)≳1.0x10¹⁷ cm^–2] and nine lower N(HI) systems [2x10¹⁴cm^–2≲N(HI)≲2x10¹⁶ cm^–2] observed in the Very Large Telescope/UV-Visual Echelle Spectrograph 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 σ_v on the absorber size L is confirmed: the majority of the analyzed systems follow the scaling relation σ_v~(N_HL)^0.3 (with N_Hbeing the total gas column density). This means that most absorbers may be related to virialized systems such as 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_☉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 [α-element/iron peak] enrichment is revealed: the absorber at z_abs=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 that are very similar to those observed in high-velocity clouds (HVCs) in the Milky Way and may be considered as high-redshift counterparts of Galactic HVCs.