Thermal and non-thermal emission in the Cygnus X region

¹ College of Physical Science and Technology, Shenyang Normal University, 110034 Shenyang, PR China
e-mail: bearwards@gmail.com
² National Astronomical Observatories, Chinese Academy of Sciences, Jia-20 Datun Road, Chaoyang District, 100012 Beijing, PR China

Received: 8 February 2013
Accepted: 23 September 2013

Abstract

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 H ii 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 β = −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 95. The thermal emission component is found to comprise 75% of the total continuum radiation at λ6 cm. Thermal diffuse emission, rather than the discrete H ii 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 H ii regions embedded in the complex standing out, but no new large SNRs brighter than ∑ _1  GHz = 3.7   ×   10^-21  W  m^-2  Hz^-1  sr^-1 are found.