SDSS J085431.18+173730.5: The First Compact Elliptical Galaxy Hosting an Active Nucleus

TL;DR

This paper reports the discovery of a rare compact elliptical galaxy with an active nucleus, hosting a supermassive black hole, and analyzes its structural properties and possible origin.

Contribution

It presents the first detailed study of a compact elliptical galaxy hosting an active nucleus, including structural analysis and black hole mass estimation.

Findings

The galaxy has a half-light radius of 490 pc and an active nucleus with broad Hα emission.

The black hole mass is estimated at 2.1×10^6 solar masses.

The galaxy's properties are consistent with known black hole-bulge relations.

Abstract

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.