# A search for extended radio emission from selected compact galaxy groups

## TL;DR

This study investigates the presence and properties of intergalactic magnetic fields in selected compact galaxy groups using radio observations, revealing their existence and potential significance in the intra-group medium.

## Contribution

First detection of intergalactic magnetic fields in specific galaxy groups using combined radio data analysis, highlighting their possible energetic importance.

## Key findings

- Magnetic fields are present in HCG 15 and HCG 60.
- No magnetic fields detected in HCG 68.
- Hints of an intergalactic bridge in HCG 44.

## Abstract

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.