Radio continuum from the most massive early-type galaxies detected with ASKAP RACS

All very massive early-type galaxies contain supermassive blackholes, but are these blackholes all sufficiently active to produce detectable radio continuum sources? We have used the 887.5 MHz Rapid ASKAP Continuum Survey DR1 to measure the radio emission from morphological early-type galaxies brighter than K_S=9.5 selected from the 2MASS Redshift Survey, HyperLEDA, and RC3. In line with previous studies, we find median radio power increases with infrared luminosity, with P_1.4 ∝ L_K^2.2, although the scatter about this relation spans several orders of magnitude. All 40 of the M_K<-25.7 early-type galaxies in our sample have measured radio flux densities that are more than 2σ above the background noise, with 1.4 GHz radio powers spanning ∼ 3 × 10²⁰ to ∼ 3× 10²⁵ W/Hz^-1. Cross-matching our sample with integral field spectroscopy of early-type galaxies reveals that the most powerful radio sources preferentially reside in galaxies with relatively low angular momentum (i.e. slow rotators). While the infrared colours of most galaxies in our early-type sample are consistent with passive galaxies with negligible star formation and the radio emission produced by active galactic nuclei or AGN remnants, very low levels of star formation could power the weakest radio sources with little effect on many other star formation rate tracers.