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We propose to build a Wide Field Infrared Explorer (WIRE) in response to NASA's 1992 Announcement of Opportunity for Small Explorers. WIRE will be capable of detecting typical starburst galaxies at a redshift of 0.5, ultraluminous infrared galaxies beyond a redshift of 2, and luminous protogalaxies beyond a redshift of 5. This instrument will survey about 100 deg$^2$ of high Galactic latitude sky at 12 and 25$\mu$m, in passbands where 20\% of the luminosity from local starbursts is radiated. WIRE will measure the 12--25$\mu$m color of the starburst galaxies, which is a powerful statistical luminosity indicator. The distribution of starburst galaxy 12--25$\mu$m colors as a function of flux density will reveal their evolutionary history and perhaps the presence of protogalaxies at high redshifts. Follow-up observations of a subset of the WIRE survey will provide a test of our assumptions in using the flux-color distribution to determine the evolution of starburst galaxies.
The objective of the WIRE mission is to answer the following questions: (1) What fraction of the luminosity of the Universe at a redshift of 0.5 and beyond is due to starburst galaxies? (2) How fast and in what ways are starburst galaxies evolving? (3) Are luminous protogalaxies common at redshifts less than 3?
During its four-month mission lifetime, WIRE will gather ample data to answer these questions and amass a catalog exceeding the size of the IRAS Point Source Catalog. If starburst galaxies are evolving at a modest pace, then a three-hour exposure will reach flux densities below 0.4 mJy, 5$\sigma$, and will be dominated by confusion noise.
WIRE is specifically designed to detect the maximum number of high-redshift starburst galaxies using the smallest, simplest instrument possible. The 28cm aperture Cassegrain telescope has no moving parts and a wide 34 $\times$ 34 arcminute field of view. It capitalizes on the 128 $\times$ 128 Si:As IBC detector arrays now available. The optics and detectors are cooled during the mission using only 3~kg of solid H$_2$. The WIRE instrument requires only a single stare-type observing mode, fixed solar panel, 35 watts of power, and a low data rate (7 kbits/sec average).
The WIRE survey will be over 500 times fainter than the IRAS Faint Source Survey at 12 and 25$\mu$m. This revolutionary gain in sensitivity over a significant part of the sky permits breakthroughs in all areas of astronomy.
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