MID - IR Surveys - The Next Generations

Using new cosmological models for galaxy evolution, predictions for the next generation of deep mid-IR surveys are presented for both the ASTRO-F space telescope (due for launch 2003) and the proposed HII/L2 mission (2010). Although ASTRO-F will be able to detect between 20,000-40,000 sources in the mid-IR, deep surveys will be severely constrained by confusion due to faint sources (due to the relatively small aperture of all IR space telescopes to date). However, HII/L2 with its larger 3.5m mirror will be able to observe to fluxes 10-100 times deeper below the present confusion limits. ASTRO-F also known as the Infrared Imaging Surveyor (IRIS) is the second infrared astronomy mission of the Japanese Institute of Space and Astronautical Science (ISAS). ASTRO-F is a 70cm cooled telescope and will be dedicated for infrared sky surveys (Onaka et al. (1998)). The ASTRO-F Richey-Chretian telescope has a 70cm aperture and is cooled to 6K, and the detectors to 1.8K, using a light weight liquid Helium Cryostat. Two 2-stage Stirling-cycle coolers ensure minimum heat flow from the outer wall of the cryostat, almost doubling the lifetime of the Helium thus allowing approximately 150l of liquid Helium to sustain the telescope for more than 400 days. Another advantage of using the mechanical coolers is that the near-infrared detectors will still be usable even after the Helium expires (providing the coolers continue to function). ASTRO-F covers wide wavelength range from the K-band to 200µm. Two focal-plane instruments are installed. The first is the Far-Infrared Surveyor (FIS, Kawada (1998)) which will survey the entire sky in the wavelength range from 50 to 200µm (Takeuchi et al. (1999), Pearson (2000)). The other focal-plane instrument is the Infrared Camera (IRC, see Table 1).