Broad absorption-line QSOs

Photoionization and radiative transfer in gas near a QSO are considered for conditions appropriate for producing broad absorption. Spectrophotometric observations of PHL 5200 and six other QSOs with known broad absorption are presented. Absorbing regions near the central continuum source require high density gas to prevent photoionzation from destroying the observed ions. Small volume filling factors are needed with the gas concentrated in dense filaments. Photoionization can produce the observed high ionization and relatively weak Lα absorption if the central source luminosity falls rapidly at frequencies above one Rydberg. Luminosity per unit frequency interval from the central source as steep as v-4 is needed. Another alternative is to have hydrogen less abundant than normal relative to the elements observed in absorption: carbon, silicon, and nitrogen. The spectra of UM139, UM141, UM232, UM275, Q1246-057, and RS23 are discussed. UM141 has very weak Lα absorption. UM275 has two broad absorption-line systems. The higher velocity system has a CIV trough about as deep as the CIV absorption in PHL 5200. This is another system where the fraction of sky covered is small. The partial covering models work well for broad absorption-line systems well detached from the emission. There is less scattered radiation in these models