SPICA: a joint infrared space observatory (Conference Presentation)

Measurements in the infrared wavelength domain allow us to assess directly the physical state and energy balance of cool matter in space, thus enabling the detailed study of the various processes that govern the formation and early evolution of stars and planetary systems in the Milky Way and of galaxies over cosmic time. Previous infrared missions, from IRAS to Herschel, have revealed a great deal about the obscured Universe, but sensitivity has been limited because up to now it has not been possible to fly a telescope that is both large and cold. Such a facility is essential to address key astrophysical questions, especially concerning galaxy evolution and the development of planetary systems. SPICA is a mission concept aimed at taking the next step in mid- and far-infrared observational capability by combining a large and cold telescope with instruments employing state-of-the-art ultra-sensitive detectors. The mission concept foresees a 2.5-meter diameter telescope cooled to below 8 K. Rather than using liquid cryogen, a combination of passive cooling and mechanical coolers will be used to cool both the telescope and the instruments. With cooling not dependent on a limited cryogen supply, the mission lifetime can extend significantly beyond the required three years. The combination of low telescope background and instruments with state-of-the-art detectors means that SPICA can provide a huge advance on the capabilities of previous missions. The SPICA instrument complement offers spectral resolving power ranging from ~50 through 11000 in the 17-230 µm domain as well as ~28.000 spectroscopy between 12 and 18 µm. Additionally, SPICA will be capable of efficient 30-37 µm broad band mapping, and small field spectroscopic and polarimetric imaging in the 100-350 µm range. SPICA will enable far infrared spectroscopy with an unprecedented sensitivity of ~5x10-20 W/m2 (5σ/1hr) - at least two orders of magnitude improvement over what has been attained to date. With this exceptional leap in performance, new domains in infrared astronomy will become accessible, allowing us, for example, to unravel definitively galaxy evolution and metal production over cosmic time, to study dust formation and evolution from very early epochs onwards, and to trace the formation history of planetary systems.