Radio AGN signatures in massive quiescent galaxies out to z=1.5

This work represents the first multi-wavelength analysis of the average IR and radio emission in 14200 quiescent galaxies out to z=3. By stacking 24um, Herschel and VLA imaging data, we reveal the widespread presence of low-luminosity radio AGN among massive galaxies of Mstar>10^11Msun out to at least z=1.5, reciprocating the fact that massive quiescent galaxies are the preferential hosts of low-lumionsity AGN. Combined with the result of low average 24um emission, we infer that only radio-mode feedback, but not (obscured) quasar-mode feedback, is at work in keeping star formation inefficient in these galaxies.