SDSS J085431.18+173730.5: The First Compact Elliptical Galaxy Hosting an
  Active Nucleus
  We report the discovery of a rare compact early-type galaxy, SDSS
J085431.18+173730.5 (hereafter cE\_AGN). It has an half light radius of R$_{e}$
= 490 pc and a brightness of M$_{r}$ = $-$18.08 mag. Optical spectroscopy
available from the Sloan Digital Sky Survey (SDSS) reveals the presence of
prominent broad-line emissions with the H$\alpha$ broad component width of
FWHM=2400 km/s. The black hole (BH) mass, as estimated from the luminosity and
width of the broad H$\alpha$ emission, is 2.1$\times$10$^{6}$ M$_{\sun}$. With
the help of surface photometry, we perform a detailed analysis of the
structural properties. The observed light distribution is best modeled with a
double S\'ersic function. Fixing the outer component as an exponential disk, we
find that the inner component has a S\'ersic index of n = 1.4. Considering the
inner component as bulge/spheroidal we find that cE\_AGN remains consistent in
both BH mass -- bulge mass relation and BH mass -- bulge S\'ersic index
relation. Given these observational properties, we discuss its possible origin
investigating the surrounding environment where it is located.
