Lensing Magnification: Implications for Counts of Submillimeter Galaxies and SZ Clusters

We study lensing magnification of source galaxies by intervening galaxy groups and clusters using a halo model approach. Halos are modeled with truncated NFW profiles with ellipticity added to their lensing potential and propagated to observable lensing statistics. The magnification probability distribution of this model compares well with numerical results from ray-tracing simulations. We apply this model to observable effects of magnification, primarily the number counts of high-redshift galaxies. Using the BLAST data for submillimeter galaxies (SMGs), we find that magnification affects steep regions of the SMG counts distribution by up to ∼ 40 %. This effect is still smaller than current errors on the counts. We consider the effect of this highredshift galaxy population on contaminating the Sunyaev-Zel’dovich (SZ) signal of massive clusters. We find that for the majority of clusters expected to be detected with ongoing SZ surveys, there is significant contamination from the Poisson noise due to background SMGs. This contribution can be comparable to the SZ increment for typical clusters and can also contaminate the SZ decrement of low mass clusters. Thus SZ observations, especially for the increment part of the SZ spectrum, need to include careful modeling of this irreducible contamination for proper mass estimation. Lensing does not enhance the contamination significantly on average, though it may do so close to cores of massive clusters or for very disturbed clusters.