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 a 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 Hα broad component width of FWHM =2400 km s^-1. The black hole (BH) mass, as estimated from the luminosity and width of the broad Hα emission, is 2.1x10⁶. 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 Sérsic function. Fixing the outer component as an exponential disk, we find that the inner component has a Sérsic index of n =1.4. Considering the inner component as bulge/spheroidal we find that cE-AGN remains consistent in both the BH mass-bulge mass relation and the BH mass-bulge Sérsic index relation. Given these observational properties, we discuss its possible origin investigating the surrounding environment where it is located.