Millimeter-band Surveys of Extragalactic Sources

Gianfranco De Zotti, Francesca Perrotta and Gian Luigi GranatoINAF – Osservatorio Astronomico di Padova, ItalyLaura SilvaINAF – Osservatorio Astronomico di Trieste, ItalyRoberto Ricci, Carlo Baccigalupi and Luigi DaneseSISSA, Trieste, ItalyLuigi ToffolattiDepartamento de F´isica, Universidad de Oviedo, SpainAbstract. Surveys at mm wavelengths emphasize rare classes of extra-galactic radio sources characterized by spectra keeping flat or inverted upto high frequencies (such as blazars, GPS sources, advection dominatedsources, or even gamma-ray burst afterglows), which are are difficult tosingle out at lower frequencies where the counts are dominated by farmore numerous populations. Such surveys may lead to the discovery ofpopulations with extreme properties, such as sources of the general GPSor blazar type but peaking at mm wavelengths, whose existence is hintedby currently available data. At relatively lower flux levels mm countsare dominated by high-redshift dusty galaxies, such as those detected bySCUBA and MAMBO surveys. These data have profound implicationsfor our understanding of the formation and early evolution of galaxies.High sensitivity surveys at cm/mm wavelengths may also detect galaxy-scale Sunyaev-Zeldovich effects due to gas heated by central active nuclei.1. IntroductionThe millimeter region is quite a special one, since its corresponds to a minimumin the spectral energy distribution of the Galaxy and of most (but not all)classes of extragalactic sources. The minimum occurs at the cross-over betweenradio emission, which generally (but not always) decreases with frequency witha power law spectrum (S