Possible Ongoing Merger Discovered by Photometry and Spectroscopy in the Field of the Galaxy Cluster PLCK G165.7+67.0

We present a detailed study of the Planck-selected binary galaxy cluster PLCK G165.7+67.0 (G165; z = 0.348). A multiband photometric catalog is generated incorporating new imaging from the Large Binocular Telescope/Large Binocular Camera and Spitzer/IRAC to existing imaging. To cope with the different image characteristics, robust methods are applied in the extraction of the matched-aperture photometry. Photometric redshifts are estimated for 143 galaxies in the 4 arcmin(2) field of overlap covered by these data. We confirm that strong-lensing effects yield 30 images of 11 background galaxies, of which we contribute new photometric redshift estimates for three image multiplicities. These constraints enable the construction of a revised lens model with a total mass of M (600 kpc) = (2.36 +/- 0.23) x 10(14) M (circle dot). In parallel, new spectroscopy using MMT/Binospec and archival data contributes thirteen galaxies that meet our velocity and transverse radius criteria for cluster membership. The two cluster components have a pair-wise velocity of less than or similar to 100 km s(-1), favoring an orientation in the plane of the sky with a transverse velocity of 100-1700 km s(-1). At the same time, the brightest cluster galaxy (BCG) is offset in velocity from the systemic mean value, suggesting dynamical disturbance. New LOFAR and Very Large Array data uncover head-tail radio galaxies in the BCG and a large red galaxy in the northeast component. From the orientation and alignment of the four radio trails, we infer that the two cluster components have already traversed each other, and are now exiting the cluster.

Automated summary

We present a detailed study of the Planck-selected binary galaxy cluster PLCK G165.7+67.0 (G165; z = 0.348). By generating a multiband photometric catalog and incorporating new spectroscopy and imaging data, we analyze the properties, members, and mass of the galaxy cluster. The results indicate that the relative velocity between the cluster components is small, with the brightest cluster galaxy showing an offset in velocity from the systemic mean value, and head-tail radio galaxies and a large red galaxy are discovered.