An AMUSING look at the host of the periodic nuclear transient ASASSN-14ko reveals a second AGN
Kochanek, C. S.; Galbany, L.; Holoien, Thomas W. -S.; Shappee, B. J.; Tucker, M. A.; Anderson, J. P.; Prieto, J. L.; Eracleous, M.; Hinkle, J. T.; Neustadt, J. M. M.; Payne, A. V.; Auchettl, K.; Auge, C.
United States, Chile, Spain, Australia
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 survey. The MUSE observations reveal that the inner region hosts two AGN separated by $1.4\pm 0.1~\rm {kpc}$ (≈1${_{.}^{\prime\prime}}$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 $\hbox{$v_{\rm {FWHM}}$} \approx 700~\hbox{km~s$^{-1}$}$ forbidden line emission, $\rm{\log _{10}(\rm{[O\,\small {III}]}/\rm{H\beta})} \approx 1.1$, 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 disc model cannot reproduce the asymmetric broad emission-line profiles in the brighter nucleus, but two non-axisymmetric disc models provide good fits to the broad emission-line profiles: an elliptical disc model and a circular disc + spiral arm model. Implications for the periodic nuclear transient ASASSN-14ko are discussed.