Physical conditions in broad and associated narrow absorption-line systemstoward APM 08279+5255

Results of a careful analysis of the absorption systems with z(abs)similar or equal to z(em) seen toward the bright, z(em) similar to 3.91,gravitation ally lensed quasar APM 08279+5255 are presented. Two of the narrow-line systems, at z(abs) = 3.8931 and z(abs) = 3.9135 show absorptions from singly ionized species with weak or no N V and O VI absor ptions at the same redshift. Absorption due to fine structure transitions o f C II and Si II (excitation energies corresponding to, respectively, 156 m u m and 34 mu m) are detected at z(abs) = 3.8931. Excitation by IR radiatio n is favored as the column density ratios are consistent with the shape of APM 08279+5255 IR spectrum. The low-ionization state of the system favors a picture where the cloud is closer to the IR source than to the UV source, supporting the idea that the extension of the IR source is larger than simi lar to 200 pc. The absence of fine structure lines at z(abs) = 3.9135 sugge sts that the gas responsible for this system is farther away from the IR so urce. Abundances are similar to 0.01 and 1 Z(circle dot) at z(abs) = 3.913 and 3.8931 and aluminum could be over-abundant with respect to silicon and carbon by at least a factor of two and five. All this suggests that whereas the z(abs) = 3.8931 system is probably located within 200 pc from the QSO and ejected at a velocity larger than 1000 km s(-1): the z(abs) = 3.9135 sy stem is farther away and part of the host-galaxy. Several narrow-line systems have strong absorption lines due to C rv, O vr and N v and very low neutral hydrogen optical depths. This probably implies metallicities Z greater than or equal to Z(circle dot) although firm concl usion cannot be drawn as the exact value depends strongly on the shape of t he ionizing spectrum. The C IV broad absorption has a complex structure with mini-BALs (width les s than or equal to 1000 km s(-1)) and narrow components superposed on a con tinuous absorption of smaller optical depth. The continuous absorption is m uch stronger in O vl indicating that the corresponding gas-component is of higher ionization than the other components in the flow and that absorption structures in the BAL-now are mainly due to density inhomogeneities. There is a tendency for mini-BALs to have different covering factors for differe nt species. It is shown that a few of the absorbing clouds do not cover all the three QSO images, especially we conclude that the z(abs) = 3.712 syste m covers only image C. Finally we identify narrow components within the BAL-flow with velocity sep arations within 5 km s(-1) of the O vl, N v and Si Iv doublet splittings su ggesting that line driven radiative acceleration is an important process to explain the out-flow.