Impact of galactic interactions on the evolution of the far-infrared–radio correlation

Abstract

A strong correlation has been known to exist between the far-infrared (FIR) and radio emission of star-forming galaxies. Observations have shown that, although scatter is present, this correlation holds over a range of redshifts and does not evolve. However, there have been a number of more recent observations, especially in higher redshift surveys, indicating the opposite. The question that then presents itself is: what is driving this evolution? In this work, we explore the possibility that the answer might be hiding in galactic interactions and revealed by morphology. We present a number of models based on the evolving number of galaxies of different morphological types, some of which could potentially explain the observed trends and scatter in general. Furthermore, we analyse a small sample of 34 submillimetre galaxies for which observations have been published and morphology classified. In this sample, we look at the FIR–radio correlation separately in galaxies of different morphological types. We find that, while for both disc and irregular star-forming galaxies there are hints of evolution of this correlation with redshift, where this evolution appears to be stronger in irregular galaxies, due to low number statistics, both samples are also consistent with no evolution, making it difficult at this point to discriminate between models. However, when analysis was performed on the combined sample, an evolving and decreasing trend was indeed found, indicating that evolution should be expected in at least one of the morphological types.