An evolution of the IR-Radio correlation?
  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. 
R. J. Beswick, T. W. B. Muxlow, H. Thrall, A. M. S. Richards, S. T.   Garrington (Jodrell Bank Centre for Astrophysics, The ...