Radio detections of IR-selected runaway stellar bow shocks
  Massive stars moving at supersonic peculiar velocities through the
interstellar medium (ISM) can create bow shocks, arc-like structures at the
interface between the stellar wind and the ISM. Many such bow shocks have been
detected and catalogued at IR wavelengths, but detections in other wavebands
remain rare. Strikingly, while electrons are expected to be accelerated in the
bow shock and their non-thermal emission may include synchrotron emission at
low frequencies, only two massive runaway stellar bow shocks have to date been
detected in the radio band. Here, we examine a sample of fifty IR-detected bow
shocks from the E-BOSS catalogues in recently released radio images from the
Rapid ASKAP Continuum Survey (RACS). We identify three confident and three
likely counterparts, as well as three inconclusive candidates requiring
confirmation via follow-up observations. These detections significantly
increase the number of known radio massive stellar bow shocks and highlight the
advantage of dedicated searches with current and next-generation radio
telescopes. We investigate the underlying radio emission mechanism for these
radio sources, finding a mix of free-free-dominated and synchrotron-dominated
systems. We also discuss the non-detected targets by putting constraints on
their emission properties and investigating their detectability with future
observations. Finally, we propose several future avenues of research to advance
the study and understanding of bow shocks at radio frequencies.
