A variable P V broad absorption line and quasar outflow energetics

Broad absorption lines (BALs) in quasar spectra identify high-velocity outflows that might exist in all quasars and could play a major role in feedback to galaxy evolution. The viability of BAL outflows as a feedback mechanism depends on their kinetic energies, as derived from the outflow velocities, column densities, and distances from the central quasar. We estimate these quantities for the quasar, Q1413+1143 (redshift z(e) = 2.56), aided by the first detection of P V lambda lambda 1118, 1128 BAL variability in a quasar. In particular, P V absorption at velocities where the C IV trough does not reach zero intensity implies that the C IV BAL is saturated and the absorber only partially covers the background continuum source (with characteristic size <0.01 pc). With the assumption of solar abundances, we estimate that the total column density in the BAL outflow is log N-H similar to 22.3 cm(-2). Variability in the P V and saturated C IV BALs strongly disfavours changes in the ionization as the cause of the BAL variability, but supports models with high column density BAL clouds moving across our lines of sight. The observed variability time of 1.6 yr in the quasar rest frame indicates crossing speeds >750 km s(-1) and a radial distance from the central black hole of less than or similar to 3.5 pc, if the crossing speeds are Keplerian. The total outflow mass is similar to 4100 M-circle dot, the kinetic energy similar to 4 x 10(54) erg, and the ratio of the outflow kinetic energy luminosity to the quasar bolometric luminosity is similar to 0.02 (at the minimum column density and maximum distance), which might be sufficient for important feedback to the quasar's host galaxy.