Can the VLA detect a radio continuum core in the nucleus of every nearby galaxy? It is crucially important to answer this question because such sources may be beacons marking the locations of supermassive black holes in galactic nuclei. By simply detecting these radio beacons, the VLA can (1) constrain counts of ``simmering", rather than ``dead", quasars in the local Universe, thereby impacting our understanding of quasar evolution; and (2) provide precise ``finding charts" for follow-up dynamical studies of black hole environments with the VLBA and HST.
A radio continuum source can mark nonthermal emission from an active nucleus. These kinds of sources are commonly found among nearby giant elliptical galaxies, with the weakest known radio elliptical being NGC3379. The radio emission from these sources most likely arises from a relativistic jet formed in the vicinity of, and energized by, a supermassive black hole. A radio continuum source can also mark a mixture of thermal and nonthermal emission from a nuclear starburst, which possibly also contains a very weak embedded active nucleus and supermassive black hole. Even the nucleus of our Galaxy, marked by the Sgr A complex and including the enigmatic source Sgr A*, falls into this category, but scaled to a distance of 8 kpc.
The enhanced VLA, with a bandwidth of 2 GHz at 4cm, could detect in only one hour a source like our Galaxy's Sgr A complex, of diameter 16 pc, but at a distance of 20 Mpc. For comparison, the current VLA would require a 10-hr integration. Thus, the enhanced VLA will make it practical, for the first time, to search the nuclei of the more than 100 northern galaxies closer than 20 Mpc for radio beacons as weak and as compact as that in the nucleus of our own Galaxy.