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Many studies have considered the roles of clouds, outflows, and turbulence inproducing the broad emission and absorption lines in the spectra of activegalactic nuclei (AGNs). However, these are often treated as separate or evencompeting models. Here, we consider the possibility that AGN clouds arecondensations formed within the thermally unstable zones of outflows and thencompare the typical sizes of such condensations with the injection scale$k_0^{-1} \sim L_0$ of turbulence, where $L_0$ is assumed to be the scaleheight of a representative global outflow model. We find that for broad lineregion (BLR) parameters, clouds are many orders of magnitude smaller than $L_0$and this has the following implication: BLR cloud dynamics can be modeled usinga local approximation through the use of multiphase turbulence simulations ofX-ray irradiated plasmas. We present the first such 3D local clumpy turbulentoutflow simulations. We show that the condensations share the same type ofselection effects characterizing the locally optimally emitting cloud (LOC)scenario, thereby offering a physical interpretation for the LOC model andaccounting for its almost uncanny successes. The ubiquitous presence ofemission line regions in AGNs can be simply explained as the natural outcome ofthere being a multiphase interval of $k$-space within the inertial range of aturbulent cascade.

The AGN broad line region as a clumpy turbulent outflow: a physical basis for LOC modeling