Extragalactic foregrounds of the cosmic microwave background: Prospects for the map mission

While the major contribution to the cosmic microwave background (CMB) anisotropies are the sought-after primordial fluctuations produced at the surface of last scattering, other effects produce secondary fluctuations at lower redshifts. Here we study the extragalactic foregrounds of the CMB in the context of the upcoming Microwave Anisotropy Probe (MAP) mission. We first survey the major extragalactic foregrounds and show that discrete sources, the Sunyaev-Zeldovich (SZ) effect, and gravitational lensing are the most dominant ones for MAP. We then show that MAP is expected to detect (> 5 σ) about 46 discrete sources directly with 94 GHz fluxes above 2 Jy. The most prominent SZ features on the CMB sky are rich clusters of galaxies. In particular, we show that the Coma Cluster will be clearly detected and marginally resolved by MAP. We then consider a cosmological population of clusters, and show that MAP should detect (> 5 σ) about 10 SZ clusters directly. The mean SZ fluxes of fainter clusters can be probed by cross-correlating MAP with cluster positions extracted from existing catalogs. For instance, a AMP-XBACs cross-correlation will be sensitive to clusters with S(94 GHz) ≳ 200 mJy, and will thus provide a test of their virialization state and a measurement of their gas fraction. Finally, we consider probing the hot gas on supercluster scales by cross-correlating the CMB with galaxy catalogs. Assuming that galaxies trace the gas, we show that a cross-correlation between the (MAP) and the Automatic Plate Measuring Facility (APM) catalog should yield a marginal detection, or at least a fourfold improvement on the COBE upper limits for the rms Compton y parameter.