The thermal and non-thermal radio emission from the galaxy

Abstract

It is shown that a detailed correlation exists between IRAS 60 µm band emission from the galactic disc and radio continuum emission measured at a similar angular resolution at 11 and 6 cm. The emission at these short radio wavelengths is predominantly from thermal bremsstrahlung in regions of ionized gas and so the strong correlation, which holds for the diffuse, extended emission as well as the discrete, compact sources, indicates that an important contribution to the 60 µm emission is associated with HII regions. Isolation of this component of the 60 µm infrared emission has involved the estimation of the zodiacal light contamination and detailed modelling of the HI-associated dust emission. The residual 60 µm emission can then be used as a tracer of radio thermal emission. On the small scale this enabled a search for new supernova remnant candidates in the 11 cm survey of Reich et al. and the 6 cm survey of Haynes et al. close to the inner Galactic Plane. On the large scale we have separated the thermal and non-thermal emission of the 408 MHz all-sky survey of Haslam et al. from the whole of the Galactic Plane and within ~ 8º of the plane. From the thermal galactic emission we have been able to estimate the average infrared excess, the total 60 µm luminosity and total mass of HII in the Galaxy. The clearer picture obtained of the non-thermal emission of the Galaxy has allowed us to improve upon previous attempts at modelling the synchrotron emission in terms of the cosmic ray electron distribution and magnetic field variation modulated by the galactic spiral structure.