A comparison of the flux density scales between the EVLA and ATCA interferometers and the Planck mission

The flux density scales at centimeter and millimeter wavelengths for ground-based telescopes (in cluding both single-dish and interferometers) is based, for frequencies higher than ~5 GHz, on observations of the planets combined with emission models, (Perley and Butler, 2011). At lower frequencies, the scales are based on observations of a small set of compact galactic and extragalactic sources whose absolute flux densities are known through observations with antennas of known gain (Baars et al., 1977). The calibration of observations of the cosmic microwave background, on the other hand, are now pinned to the known large-scale dipole patterns in the CMB induced by solar and Earth orbital velocity (e.g., Planck Collaboration, 2011). The flux density scale of these experiments for unresolved sources is then determined from the beam shape. It is clearly of interest to compare results from these independent scales, both to confirm the accuracy of the models utilized in setting the ground-based scales, and to resolve a reported discrepancy between the ATCA and EVLA scales (Murphy et al., 2010,[4] Sajina et al., 2011,[5]). In December 2010 we set up an experiment to permit an accurate comparison by observing with the EVLA a set of 21 compact extragalactic sources, and with the ATCA a subset of these, all of which were being observed by ESA´s Planck satellite at the same time. Near-simultaneous observations are required by the intrinsic variability of these objects. A larger-scale comparison involving several ground-based instruments and a larger set of sources is underway (see Massardi et al. 2011, [6]). In this presentation, we will report on our preliminary results from these observations.