Galactic synchrotron emission at high frequencies

The search for structure in the cosmic microwave background (CMB) needs to take into account the Galactic background contribution. The potential of using existing maps at 408 and 1420 MHz to determine this correction at high frequencies is examined. It is found that a significant part of the high Galactic latitude structure evident in these maps is due to systematic effects connected with the original mode of observation. A method of identifying and removing some of this systematic structure is presented. The high-latitude section of the Dec. = + 40 degrees strip is examined to identify common synchrotron structure at 408 and 1420 MHz using T-T plots; the features identified have temperature spectral indices (T-b proportional to v(-beta)) in the range beta=2.8-3.2. A comparison of these maps with 10.4-GHz data obtained with the Tenerife CMB radiometer shows no common structure at high Galactic latitudes. We conclude that low-frequency observations are not good indicators of high-frequency synchrotron emission at high Galactic latitude. Direct observations over a range of frequencies are essential in searches for CMB structure where a precision of 10 mu K or better is required.