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Quasar feedback models often predict an expanding hot gas bubble which drivesa galaxy-scale outflow. In many circumstances this hot gas radiatesinefficiently and is therefore difficult to observe directly. We present anindirect method to detect the presence of a hot bubble using hydrostaticphotoionization calculations of the cold (~10^4 K) line-emitting gas. Wecompare our calculations with observations of the broad line region, the innerface of the torus, the narrow line region (NLR), and the extended NLR, and thusconstrain the hot gas pressure at distances 0.1 pc -- 10 kpc from the center.We find that emission line ratios observed in the average quasar spectrum areconsistent with radiation-pressure-dominated models on all scales. On scales<40 pc a dynamically significant hot gas pressure is ruled out, while on largerscales the hot gas pressure cannot exceed six times the local radiationpressure. In individual quasars, ~25% of quasars exhibit NLR ratios that areinconsistent with radiation-pressure-dominated models, though in these objectsthe hot gas pressure is also unlikely to exceed the radiation pressure by anorder of magnitude or more. The derived upper limits on the hot gas pressureimply that the instantaneous gas pressure force acting on galaxy-scale outflowsfalls short of the time-averaged force needed to explain the large momentumfluxes \dot{p} >> L_AGN/c inferred for galaxy-scale outflows. This apparentdiscrepancy can be reconciled if optical quasars previously experienced aburied, fully-obscured phase during which the hot gas bubble was moreeffectively confined and during which galactic wind acceleration occurred.

Constraining the dynamical importance of hot gas and radiation pressure in quasar outflows using emission line ratios