Description
At Jodrell Bank we have built a special purpose instrument to make a low resolution (23 degrees), but absolutely calibrated, map of the sky at a wavelenth of around 21 cm. Why? Firstly, existing maps which are used as templates for synchrotron emission in CMB analyses are limited in their usefulness by systematic calibration errors. A well-calibrated map can be used to bootstrap these higher resolution maps to make them more suitable for purpose, including understanding the origin of Galactic radio emission. Secondly, there is a controversial claim that there is a yet unexplained low frequency radio background – the ARCADE 2 excess. Is it of Galactic or of cosmological origin? In this talk I will describe the two-horn instrument we have built which is specifically designed to produce a map calibrated to better than 0.1K. I will focus on the calibration scheme we adopted. The fist results from a single declination scan will be presented that demonstrate the potential of the instrument. As we proceed multiple scans will be used to build up a map of the northern sky.
