Extended coronal line emission and new clues to a possible dual AGN in the merger J1356+1026

Merging luminous galaxies are ideal laboratories for studying some of the most extreme astrophysical phenomena. The local (z=0.1232) obscured quasar J1356+1026 has two nuclei, North and South (J1356N and J1356S), but despite numerous efforts, J1356S had not yet been confirmed as an AGN . Based on the superb sensitivity and spatial resolution of the MIRI/MRS instrument on board the JWST, we present new evidence suggesting that J1356S may indeed host an AGN with ̊m log L_ ̊m bol =43.4±^ 0.6 _ 0.5 erg s^ -1 . This is supported by the detection of strong coronal line emission at this location and by a spectral shape that differs from that of J1356N and those of the narrow-line region. Aided by the spatially resolved information of MIRI/MRS and VLT/SINFONI, we also found that the high-ionization gas, traced by the coronal lines Ne v 14.3 μm and Si vi 1.963 μm, extends from sim13-15.5 kpc. This is likely a lower limit of the true extension, as suggested by the comparison with optical imaging from HST. The extended Ne v emission can be accounted for by photoionization from the quasar in J1356N in a relatively low-density environment, ranging from ̊m n_ełeq 2000-3800 cm^ -3 in J1356N and ̊m n_ełeq 600-1200 cm^ -3 in J1356S and the narrow-line region, as measured from the Ne v 14.3 μm and 24.3 μm lines.