An evolution of the IR-Radio correlation at very low flux densities?

TL;DR

This study extends the infrared-radio correlation to very faint radio sources using deep observations, revealing a possible deviation at the lowest flux densities that impacts star-formation measurements.

Contribution

It provides the first detailed analysis of the IR-radio correlation at microJy flux densities, suggesting a deviation that could affect star-formation rate estimations in faint galaxies.

Findings

Detection of a small deviation from the correlation at the faintest IR flux densities.

Evidence of MIR emission suppression in faint star-forming galaxies.

Implications for using MIR or radio as star-formation tracers at low luminosities.

Abstract

In this paper we investigate the radio-MIR correlation at very low flux densities using extremely deep 1.4 GHz sub-arcsecond angular resolution MERLIN+VLA observations of a 8'.5 by 8'.5 field centred upon the Hubble Deep Field North, in conjunction with Spitzer 24micron data. From these results the MIR-radio correlation is extended to the very faint (~microJy) radio source population. Tentatively we detect a small deviation from the correlation at the faintest IR flux densities. We suggest that this small observed change in the gradient of the correlation is the result of a suppression of the MIR emission in faint star-forming galaxies. This deviation potentially has significant implications for using either the MIR or non-thermal radio emission as a star-formation tracer of very low luminosity galaxies.