2001MNRAS.324..999P

We present basic observational strategies for ASTRO-F [also known as the Infra-Red Imaging Surveyor (IRIS)] to be launched in 2004 by the Japanese Institute of Space and Astronautical Science (ISAS). We examine two survey scenarios, a deep ∼1deg² survey reaching sensitivities an order of magnitude below all but the deepest surveys performed by ISO in the mid-IR, and a shallow ∼18deg² mid-IR (7-25µm in six bands) covering an area greater than the entire area covered by all ISO mid-IR surveys. Using two cosmological models, the number of galaxies predicted for each survey is calculated. The first model uses an enhancement of a classical (1+z)^3.1 pure luminosity evolution model by Pearson & Rowan-Robinson. The second model incorporates a strongly evolving ultraluminous infrared galaxy component. For the deep survey, between 20000 and 30000 galaxies should be detected in the shortest wavebands, and ~5000 in the longest (25-µm) band. It is predicted that the shallow survey will detect of the order of 100000-150000 sources. We find that for both ASTRO-F and other small-aperture space telescopes, confusion due to faint sources may be severe, especially at the longest mid-IR wavelengths. Using the exceptional range of observational options provided by ASTRO-F (nine wavelength filters and spectroscopic ability from 2.2 to 25µm), we show that by combining the mid-IR observations with the near-IR camera on ASTRO-F, both the different galaxy populations and rough photometric redshifts can be distinguished in the colour-colour plane. In its role as a surveyor (plus near-IR spectroscopic ability) ASTRO-F will complement well the SIRTF space observatory mission.