Far-Ir and MM Properties of Quasars

We use photometric data, from the optical to the mm for a large sample of optically selected radio-quiet quasars, at low and high redshifts, to test emission models from circum-nuclear dusty torii around them. Model parameters, such as dust mass, temperature distributions and torus sizes are inferred, under the assumption that the dust is heated only by the central nuclear source. Dependences of best-fit parameters on luminosity and redshift are studied and the contribution of dust in the host galaxy to the observed fluxes is briefly mentioned. Only tentative conclusions can be drawn from this yet large dataset and detailed modelling, because crucial spectral information is missing at wavelengths where the QSO dust emission is more prominent, i.e. at $\lambda \simeq 50$ to 600 $\mu m$. Poor information in this wavelength range affects our understanding not only of the high-redshift objects, but also of the low-redshift sample. We then expect fundamental contributions by the FIRST mission in this field, which is obviously related to the more general one of galaxy formation.