A THICK REFLECTION NEBULA ILLUMINATED BY A POWER-LAW

We present the results of modelling the energy distribution of a power law reflected by a dusty cloud. We explore in a fully consistent mann er the case in which the reflecting nebula is of considerable optical depth. We apply the model to the observations of the detached emission line cloud at 8 kpc from the nucleus of Pks 2152-69 for which continu um flux measurements exist up to the far UV. Our results for the thick case qualitatively agree with the results of Fosbury et al. (1991) (w ho studied the optically thin case) in that we also need a population of grain sizes dominated by small grains (smaller on average than in m odels of the standard extinction curve) in order to reproduce the ener gy distribution of the detached continuum source. We model the high ex citation emission line spectrum of the cloud using the code MAPPINGS. Photoionization calculations in which the ionized gas contains the ref lecting dust can easily reproduce the high electronic temperature as w ell as the apparent case B Lyalpha/Hbeta ratio observed in the detache d cloud, confirming that dust is a workable hypothesis for explaining the Lyalpha emission and the blue extended light detected around many high redhift radio galaxies.