A Multiwavelength Portrait of the 3C 220.3 Lensed System

Abstract

The 3C 220.3 system is a rare case of a foreground narrow-line radio galaxy (“galaxy A,” zₐ = 0.6850) lensing a background submillimeter galaxy (zₛₘG₁ = 2.221). New spectra from MMT/Binospec confirm that the companion galaxy (“galaxy B”) is part of the lensing system with zB = 0.6835. New threecolor 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, higher than previously calculated. Deeper Chandra imaging shows extended X-ray emission but no evidence for a point X-ray 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 typical for radio galaxies.