PREFACE

During the past decades, the observation of the diffuse radio emission from the Galaxy has regained attention. In the 1950s, the first full-sky radio surveys were done at frequencies between 100 and 400 MHz. These observations, albeit at low angular resolution of 20 , revealed the basic Galactic structure and the presence of ‘spurs’ of emission. Some of the physics of the interstellar medium (ISM) was also revealed by these surveys. The nonthermal synchrotron emission coming from individual supernova remnants (SNRs) and also from the diffuse ISM provides information about the cosmic rays propagation and magnetic fields on the Galaxy. The brightness temperature and spectra of HII regions that are seen in absorption at low frequencies can be used to study the density and temperature of the gas in star forming regions. More recently, observations of the Cosmic Microwave Background (CMB) have reactivated the interest in the diffuse radio sky. The CMB is observed in the frequency range between 10 and 300 GHz and within this range there is strong emission from our Galaxy, both diffuse and from compact objects. As the brightest point sources can be masked out in the CMB analysis, the diffuse emission presents the greatest problem for CMB cosmology and its understanding and removal is critical. The importance of this foreground emission analysis was recently demonstrated with the publicized announcement by the BICEP2 team. They had claimed the detection of the B-mode polarisation pattern in the CMB, which would have major implications for cosmology, since gravitational wave B-modes are expected to be produced during the inflationary process when the Universe was less than 10 32 s old. Observations by the Planck satellite later showed that the polarised signal that the BICEP2 team reported as cosmological B-modes, was produced instead by Galactic dust. The search for B-modes continues and a number of ground-based experiments are measuring the polarised sky with even greater precision than BICEP2 and Planck. Balloon-borne and satellite experiments are also planned for the near future, so the necessity for an accurate quantification of the polarised foreground emission at 100 GHz is essential.