Metal abundances and kinematics of quasar absorbers - II. Absorption systems toward Q0347-3819 and APM BR J0307-4945

Abstract

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.