How many active galaxies and QSOs will future Space Missions detect ?

Averaged spectral energy distributions (SEDs) of active and starburst galaxies from the 12μm sample in the Local Universe and quasars, from an optically selected sample at a mean redshift 〈z〉=0.7 are built from optical, near-IR and far-IR (IRAS and ISO) photometric observations. These SEDs are then used to predict at various redshifts the number of Seyfert type 1 and type 2, starburst, normal galaxies, and quasars, that will be detected by future Space Missions dedicated to far-infrared and submillimeter astronomy, like SIRTF and Herschel. These predictions are then compared with the expected capabilities and detection limits of future deep far-IR surveys. Possible ways to identify AGN candidates on far-IR colour-colour plots for follow-up observations are then explored. Subject headings: AGN active galaxies: ISM, photometry ISM: dust, extinction, Quasars: general continuum infrared: galaxies, galaxies: active – photometry – Seyfert – starburst