Discovery of a Flat-Spectrum Radio Nucleus in NGC 3115

Abstract: The early-type galaxy NGC 3115, at a distance of 10.2 Mpc, hosts the nearest billion-solar-mass black hole. Wong et al. recently inferred a substantial Bondi accretion rate near the black hole. Bondi-like accretion is thought to fuel outflows, which can be traced through their radio emission. This paper reports the discovery of a radio nucleus in NGC 3115, with a diameter less that 0.17 arcsec (8.4 pc), a luminosity at 8.5 GHz of 3.1 x 10^35 ergs/s and a flat spectrum (alpha = -0.23+/-0.20, flux density ~ frequency^alpha). The radio source coincides with the galaxy's photocenter and candidate X-ray nucleus. The emission is radio-loud, suggesting the presence of an outflow on scales less than 10 pc. On such scales, the Bondi accretion could be impeded by heating due to disruption of the outflow.