  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.
