An evolution of the IR-Radio correlation?

TL;DR

This study investigates the radio-MIR correlation at very low flux densities using deep radio and infrared observations, revealing a potential deviation at the faintest levels that could impact star-formation measurements.

Contribution

It extends the radio-MIR correlation to microJy flux levels and suggests a possible deviation in faint star-forming galaxies, which is a novel insight.

Findings

Extended the correlation to microJy radio sources

Detected a small deviation at the faintest MIR sources

Implications for star-formation tracers at low luminosities

Abstract

Using extremely deep (rms 3.3 microJy/bm) 1.4GHz sub-arcsecond resolution MERLIN + VLA radio observations of a 8'.5 by 8'.5 field centred upon the Hubble Deep Field North, in conjunction with Spitzer 24 micron data we present an investigation of the radio-MIR correlation at very low flux densities. By stacking individual sources within these data we are able to extend the MIR-radio correlation to the extremely faint (~microJy and even sub-microJy) radio source population. Tentatively we demonstrate a small deviation from the correlation for the faintest MIR sources. 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 at low luminosities.