Enigmatic Emission Structure around Mrk 783: Cross-Ionization of a Companion 100 kpc Away

Mrk 783 is a narrow-line Seyfert 1 galaxy that possesses a relatively large two-sided radio emission extending up to 14 kpc from the active nucleus possibly connected with a large-scale ionized gas emission. We obtained a deep [O III] image that revealed an extended system of emission knots and diffuse ionized gas surrounding the main galaxy. The highly-excited gas is related not only to the radio structure, but also to tidal features illuminated by the active nucleus radiation up to the projected distance of 41 kpc as it follows from the emission lines' intensities and kinematics derived from the long-slit spectroscopic data. Moreover, the part of the disk of the companion galaxy SDSS J130257.20+162537.1, located at ∼99 kpc projected distances to the north of Mrk 783, also falls in the AGN ionizing cone. It is possiblethat Mrk 783 can be considered as 'Hanny's Voorwerp precursor', i.e., a galaxy that demonstrates signs of sequential switching from radio-loud to radio-quiet nuclear activity, in the moment before its ionization luminosity falls.