An Amusing Look at the Host of the Periodic Nuclear Transient ASASSN-14ko Reveals a Second AGN
Abstract
We present Multi-Unit Spectroscopic Explorer (MUSE) integral-field spectroscopy of ESO 253-G003, which hosts a known Active Galactic Nucleus (AGN) and the periodic nuclear transient ASASSN-14ko, observed as part of the All-weather MUse Supernova Integral-field of Nearby Galaxies (AMUSING) survey. The MUSE observations reveal that the inner region hosts two AGN separated by 1.40.1~kpc (≈ 1.\!\!7). The brighter nucleus has asymmetric broad, permitted emission-line profiles and is associated with the archival AGN designation. The fainter nucleus does not have a broad emission-line component but exhibits other AGN characteristics, including vFWHM≈ 700~km~s-1 forbidden line emission, 10([OIII]/Hβ) ≈ 1.1, and high excitation potential emission lines such as [Fe~VII]~λ6086 and He~II~λ4686. The host galaxy exhibits a disturbed morphology with large kpc-scale tidal features, potential outflows from both nuclei, and a likely superbubble. A circular relativistic disk model cannot reproduce the asymmetric broad emission-line profiles in the brighter nucleus, but two non-axisymmetric disk models provide good fits to the broad emission-line profiles: an elliptical disk model and a circular disk + spiral arm model. Implications for the periodic nuclear transient ASASSN-14ko are discussed.