Thermal and non-thermal emission in the Cygnus X region

Context. Radio continuum observations detect non-thermal synchrotron and thermal bremsstrahlung radiation. Separation of the two different emission components is crucial for studying the properties of the Galactic interstellar medium. The Cygnus X region is one of the most complex areas in the radio sky, which contains a number of massive stars and HII regions on the diffuse thermal and non-thermal background. More supernova remnants (SNRs) are expected to be discovered. Aims. We aim to develop a method that can properly separate the non-thermal and thermal radio continuum emission and apply it to the Cygnus X region. The result can be used to study the properties of different emission components and search for new SNRs in the complex. Methods. Multi-frequency radio continuum data from large-scale surveys were used to develop a new component-separation method. Spectral analysis was done pixel-by-pixel for the non-thermal synchrotron emission with a realistic spectral index distribution and a fixed spectral index of beta = -2.1 for the thermal bremsstrahlung emission. Results. With the new method, we separate the non-thermal and thermal components of the Cygnus X region at an angular resolution of 9'.5. The thermal emission component is found to comprise 75% of the total continuum radiation at lambda 6 cm. Thermal diffuse emission, rather than the discrete HII regions, is found to be the major contributor to the entire thermal budget. A smooth non-thermal emission background of 100 mK T-b is found. We successfully make the large-extent known SNRs and the HII regions embedded in the complex standing out, but no new large SNRs brighter than Sigma(I GHz) = 3.7 x 10(-21) W m(-2) Hz(-1) sr(-1) are found.