2012ApJ...753..103N

We present the results of deep, high-resolution, 5 GHz Expanded Very Large Array (EVLA) observations of the nearby, dwarf lenticular galaxy and intermediate-mass black hole candidate (M_BH∼ 4.5x10⁵ M_☉), NGC 404. For the first time, radio emission at frequencies above 1.4 GHz has been detected in this galaxy. We found a modestly resolved source in the NGC 404 nucleus with a total radio luminosity of 7.6±0.7x10¹⁷ W Hz^–1 at 5 GHz and a spectral index from 5 to 7.45 GHz of α = -0.88 ±0.30. NGC 404 is only the third central intermediate-mass black hole candidate detected in the radio regime with subarcsecond resolution. The position of the radio source is consistent with the optical center of the galaxy and the location of a known, hard X-ray point source (L_X∼ 1.2x10³⁷ erg/s). The faint radio and X-ray emission could conceivably be produced by an X-ray binary, star formation, a supernova remnant, or a low-luminosity active galactic nucleus powered by an intermediate-mass black hole. In light of our new EVLA observations, we find that the most likely scenario is an accreting intermediate-mass black hole, with other explanations being either incompatible with the observed X-ray and/or radio luminosities or statistically unlikely.