The Binary Nucleus in VCC 128: A Candidate Supermassive Black Hole in a Dwarf Elliptical Galaxy

Abstract

{\it Hubble Space Telescope} (\hst) Wide Field Planetary Camera 2 ({\it WFPC2}) images of the Virgo Cluster dwarf elliptical galaxy VCC 128 reveal an apparently double nucleus. The two components, which are separated by $\sim 32$ pc in projection, have the same magnitude and color. We present a spectrum of this double nucleus and show that it is inconsistent with one or both components being emission-line background objects or foreground stars. The most likely interpretation is that, as suggested by \citet{lauer_etal_96} for the double nucleus in NGC 4486B, we are seeing a nuclear disk surrounding a supermassive black hole. This is only the second time an early-type dwarf (dE/dSph) galaxy has been suggested to host a SMBH.