Calibration Issues in the Search for Large-Scale Anisotropies in the 87 Green Bank and Parkes-Mit-Nrao Surveys

Until recently, there were no large scale radio surveys which were sensitive enough to have a sufficient number of sources to detect a dipole anisotropy. The 87 Green Bank (87GB) (Gregory and Condon, 1991) and Parkes-MIT-NRAO (PMN) (Griffith, 1993; Griffith et al., 1994, 1995; Wright et al., 1994) radio surveys are the first such efforts and are the most complete radio surveys to date. We would like to analyze the source counts in these surveys in order to test the isotropy of the sky distribution of extragalactic sources at cosmological redshifts. Of particular interest is a dipole anisotropy, which could arise from local motion with respect to the rest frame of extragalactic radio sources. Any detected anisotropy will give information about the source sky distribution at a redshift of z ∼ 1 (Condon, 1988), an epoch between the COBE observations at z ∼ 1000 and the local universe.