Searching for the magnetised Tidal Dwarf Galaxies in Hickson Compact Groups: HCG 26, 91, and 96

TL;DR

This study investigates the presence of magnetic fields in tidal dwarf galaxy candidates within Hickson Compact Groups using radio continuum data, revealing complex origins of radio emission and star formation history.

Contribution

It provides the first detailed analysis of magnetic fields in TDG candidates in Hickson groups, combining multi-frequency radio data with optical and infrared observations.

Findings

Radio emission coincident with HCG 91i suggests possible magnetic fields of 11-16 μG.

Star formation rate from radio flux exceeds Hα estimates by two orders of magnitude.

Radio emission may originate from a background source or reflect past star formation activity.

Abstract

In this work, archive 1.4 and 4.86 GHz radio continuum data from the VLA were re-reduced and, together with the 1.4 GHz maps from the NVSS, investigated for the presence of a detectable, non-thermal continuum radio emission that could be associated with the TDG candidates in HCG 26, 91, and 96. Radio emission highly coincident with the optical and $\rm H_{\alpha}$ emission maxima of the TDG candidate HCG 91i (estimated physical separation of less than 150 pc) was revealed. Should this emission be intrinsic to this object, it would imply the presence of a magnetic field as strong as 11--16 $\mu$G -- comparable to that found in the most radio-luminous, star-forming dwarf galaxies of non-tidal origin. However, the star formation rate derived for this object using the radio flux is about two orders of magnitude higher, than the one estimated from the $\rm H_{\alpha}$ data. Analysis of the auxiliary radio, ultraviolet and infrared data suggests that either the radio emission originates in a background object with an aged synchrotron spectrum (possibly a GHz-peaked source), or the $\rm SFR_{H_{\alpha}}$ estimate is lower due to the fact that it traces the most recent star formation, while most of the detected radio emission originated when what is known as HCG 91i was still a part of its parent galaxy. The latter scenario is supported by a very large stellar mass derived from 3.6 and 4.5 $\mu$m data, implying high star formation in the past.