Classify the NE extension emission in the A2061–A2067 system

Classify whether the diffuse radio emission in the northeast (NE) extension of Abell 2061 is a radio bridge toward Abell 2067 or a natural extension of the Abell 2061 radio halo, based on multiwavelength evidence.

Background

Deep LOFAR HBA observations at 144 MHz reveal diffuse emission extending ~800 kpc from the radio halo in Abell 2061 toward Abell 2067. Abell 2061 hosts a confirmed radio halo and relic, whereas Abell 2067 shows no diffuse radio halo.

Analyses of radio and X-ray radial profiles show a systematic excess of radio emission beyond ~2.5 e-folding radii of the A2061 halo in the NE direction and an X-ray excess beyond the known plume, suggesting either filament-related emission (a radio bridge) or a halo elongation tied to dynamical activity.

Point-to-point radio/X-ray surface brightness correlations show a sub-linear relation for the whole system but no clear correlation within the NE extension alone. Three scenarios are considered: infalling group (consistent with a bridge), slingshot tail (consistent with a halo extension), and exiting group (disfavored). The available data do not uniquely determine the origin of the NE extension.