2024ApJ...974..171H

The 3C 220.3 system is a rare case of a foreground narrow-line radio galaxy (“galaxy A,” z_A = 0.6850) lensing a background submillimeter galaxy (z_SMG = 2.221). New spectra from MMT/Binospec confirm that the companion galaxy (“galaxy B”) is part of the lensing system with z_B = 0.6835. New three-color Hubble Space Telescope (HST) data reveal a full Einstein ring and allow a more precise lens model. The new HST images also reveal extended emission around galaxy A, and the spectra show extended [O II] emission with irregular morphology and complex velocity structure. All indications are that the two lensing galaxies are a gravitationally interacting pair. Strong [O II] emission from both galaxies A and B suggests current star formation, which could be a consequence of the interaction. This would indicate a younger stellar population than previously assumed and imply smaller stellar masses for the same luminosity. The improved lens model and expanded spectral energy distributions have enabled better stellar mass estimates for the foreground galaxies. The resulting dark matter fractions are ∼0.8, which are higher than previously calculated. Deeper Chandra imaging shows extended X-ray emission but no evidence for an X-ray point source associated with either galaxy. The detection of X-rays from the radio lobes of 3C 220.3 allows an estimate of ∼3 nT for the magnetic fields in the lobes, a factor of ∼3 below the equipartition fields, as is typical for radio galaxies.