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IRAS conducted the first unbiased all-sky survey (or almost, covering 98% of the sky), detecting point sources down to 0.2 mJy or fainter at 12, 25 and 60 µm, and down to 1 Jy at 100 µm (Beichman et al. 1986; Moshir et al. 1992). IRAS also carried out a spectroscopic survey with a resolving power of 20 between 7.5 and 23 µm, for objects brighter than 10 Jy or so. IRAS doubled the amount of existing infrared data at lambda > 5 µm within its first hour of observation. The IRAS mission lasted ten months. It resulted in a data set which completely defined our knowledge of normal galaxies at lambda > 5 µm until the launch of ISO. The Kuiper Airborne Observatory (KAO) contributed its share to the field, but because it was limited to high surface brightness objects, its impact on normal galaxies remained minor.

IRAS measured fluxes for nearly 60,000 galaxies, perhaps half of which were previously uncatalogued. It allowed detailed studies of many nearby galaxies, and of course of the Milky Way, establishing several crucial connections between global properties of galaxies and specific aspects and phases of the local ISM. Some of the contributions of IRAS to normal galaxies statistical properties are summarized in the following three subsections. See also the early review by Soifer, Houck & Neugebauer (1987), and the overviews in the 1991 Les Houches Summer School proceedings.