  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.
