A Multiwavelength Portrait of the 3C 220.3 Lensed System

TL;DR

This study presents a detailed multiwavelength analysis of the 3C 220.3 gravitational lensing system, revealing complex galaxy interactions, refined mass estimates, and insights into the system's star formation, dark matter, and magnetic fields.

Contribution

The paper provides the first comprehensive multiwavelength portrait of 3C 220.3, including improved lens modeling, stellar mass estimates, and magnetic field measurements, highlighting galaxy interactions and their effects.

Findings

The lensing galaxies are a gravitationally interacting pair.

Dark matter fractions are approximately 0.8, higher than previous estimates.

Magnetic fields in the radio lobes are about 3 nT, below equipartition values.

Abstract

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 ($z_{{\rm SMG1}} = 2.221$). 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 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 [OII] emission with irregular morphology and complex velocity structure. All indications are that the two lensing galaxies are a gravitationally interacting pair. Strong [OII] 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.