A search for extended radio emission from selected compact galaxy groups
  Context. Studies on compact galaxy groups have led to the conclusion that a
plenitude of phenomena take place in between galaxies that form them. However,
radio data on these objects are extremely scarce and not much is known
concerning the existence and role of the magnetic field in intergalactic space.
Aims. We aim to study a small sample of galaxy groups that look promising as
possible sources of intergalactic magnetic fields; for example data from radio
surveys suggest that most of the radio emission is due to extended, diffuse
structures in and out of the galaxies. Methods. We used the Effelsberg 100 m
radio telescope at 4.85 GHz and NRAO VLA Sky Survey (NVSS) data at 1.40 GHz.
After subtraction of compact sources we analysed the maps searching for
diffuse, intergalactic radio emission. Spectral index and magnetic field
properties were derived. Results. Intergalactic magnetic fields exist in groups
HCG 15 and HCG 60, whereas there are no signs of them in HCG 68. There are also
hints of an intergalactic bridge in HCG 44 at 4.85 GHz. Conclusions.
Intergalactic magnetic fields exist in galaxy groups and their energy density
may be comparable to the thermal (X-ray) density, suggesting an important role
of the magnetic field in the intra-group medium, wherever it is detected.
