Quasar-driven winds on the scale of the host galaxy are often invoked to explain why star formation appears to be suppressed in massive galaxies. However, the physical mechanism via which such large-scale outflows are accelerated is still unclear. I will demonstrate that the nature of the wind acceleration mechanism can be constrained from the ratios of emission lines that originate from the cool (T~10^4K) gas illuminated by the AGN. I will show that observed line ratios in UV-selected quasars suggest that radiation pressure dominates the acceleration in these objects at all distance scales, and that this result is apparently in conflict with the large momentum outflow rates measured in quasar winds.
// by Adi