Millisecond Pulsars Modify the Radio-SFR Correlation in Quiescent
  Galaxies
  The observed correlation between the far-infrared and radio luminosities of
galaxies illustrates the close connection between star formation and cosmic-ray
production. Intriguingly, recent gamma-ray observations indicate that
recycled/millisecond pulsars (MSPs), which do not trace recent star formation,
may also efficiently accelerate cosmic-ray electrons. We study the contribution
of MSPs to the galactic non-thermal radio emission, finding that they can
dominate the emission from massive quiescent galaxies. This model can explain
recent LOFAR observations that found a peculiar radio excess in galaxies with
high stellar masses and low star-formation rates. We show that MSP-based models
provide a significantly improved fit to LOFAR data. We discuss the implications
for the radio-FIR correlation, the observation of radio excesses in nearby
galaxies, and local electron and positron observations.
