How Massive are BALQSO Winds?

We are involved in a program to derive properties of broad absorption line (BAL) winds in quasars using combined UV and X-ray observations. A major obstacle is large uncertainties in the derived BAL column densities because of partial coverage of the background light source. In this preliminary report, we circumnavigate those uncertainties by making a simple assumption – that the relative metal abundances are roughly solar. In this case, the P v λλ1118,1128 multiplet should have at least 500 times lower optical depth than C iv λλ1549,1551. Nonetheless, a P v BAL is present in at least half of the well-measured BALQSOs we studied. We conclude that the strong lines of abundant species like C iv are typically very optically thick. The total BAL column densities are NH >∼ 10 22 cm (for solar overall metallicity), and they might be comparable to the X-ray absorbers, of order 10 cm, if the BAL gas is sufficiently ionized. If the column densities in outflowing BAL gas are, in fact, as large as the X-ray absorbers, it would present a serious challenge to models of radiatively-driven BAL winds.