Extragalactic Foregrounds of the Cosmic Microwave Background: Prospects for theMAPMission

(Abridged) While the major contribution to the Cosmic Microwave Background(CMB) anisotropies are the sought-after primordial fluctuations produced at thesurface of last scattering, other effects produce secondary fluctuations atlower redshifts. Here, we study the extragalactic foregrounds of the CMB in thecontext of the upcoming MAP mission. We first survey the major extragalacticforegrounds and show that discrete sources, the Sunyaev-Zel'dovich (SZ) effect,and gravitational lensing are the most dominant ones for MAP. We then show thatMAP will detect (>5 sigma) about 46 discrete sources and 10 SZ clustersdirectly with 94 GHz fluxes above 2 Jy. The mean SZ fluxes of fainter clusterscan be probed by cross-correlating MAP with cluster positions extracted fromexisting catalogs. For instance, a MAP-XBACs cross-correlation will besensitive to clusters with S(94GHz)>200mJy, and will thus provide a test oftheir virialization state and a measurement of their gas fraction. Finally, weconsider probing the hot gas on supercluster scales by cross-correlating theCMB with galaxy catalogs. Assuming that galaxies trace the gas, we show that across-correlation between MAP and the APM catalog should yield a marginaldetection, or at least a four-fold improvement on the COBE upper limits for therms Compton y-parameter.