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Mystery solved: discovery of extended radio emission in the merging galaxy cluster Abell 2146

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Hlavacek-Larrondo, J 
Gendron-Marsolais, M-L 
Fecteau-Beaucage, D 
van Weeren, RJ 
Russell, HR 


Abell 2146 (z = 0.232) is a massive galaxy cluster currently undergoing a spectacular merger in the plane of the sky with a bullet-like morphology. It was the first system in which both the bow and upstream shock fronts were detected at X-ray wavelengths (Mach ∼2), yet deep Giant MetreWave Telescope 325 MHz observations failed to detect extended radio emission associated with the cluster as is typically seen in such systems. We present new, multiconfiguration 1–2 GHz Karl G. Jansky Very Large Array (VLA) observations of Abell 2146 totalling 16 h of observations. These data reveal for the first time the presence of an extended (≈850 kpc), faint radio structure associated with Abell 2146. The structure appears to harbour multiple components, one associated with the upstream shock that we classify as a radio relic and one associated with the subcluster core that is consisted as being a radio halo bounded by the bow shock. The newly detected structures have some of the lowest radio powers detected thus far in any cluster (P1.4 GHz, halo = 2.4 ± 0.2 × 1023 W Hz−1 and P1.4 GHz, relic = 2.2 ± 0.2 × 1023 W Hz−1). The flux measurement of the halo, as well as its morphology, also suggests that the halo was recently created (≈0.3 Gyr after core passage), consistent with the dynamical state of the cluster. These observations demonstrate the capacity of the upgraded VLA to detect extremely faint and extended radio structures. Based on these observations, we predict that many more radio relics and radio haloes in merging clusters should be detected by future radio facilities such as the Square Kilometre Array.



acceleration of particles, radiation mechanisms: non-thermal, shock waves, galaxies: clusters: individual: Abell 2146, radio continuum general, X-rays: galaxies: clusters

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Monthly Notices of the Royal Astronomical Society

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Oxford University Press
European Research Council (340442)
Science and Technology Facilities Council (ST/P004636/1)
Science and Technology Facilities Council (ST/N000927/1)
JHL is supported by NSERC through the discovery grant and Canada Research Chair programmes, as well as FRQNT through the new university researchers start up programme. MLGM is supported by NSERC through the NSERC Post-graduate Scholarship Doctoral programme (PGSD). DFB is supported by NSERC, through the summer internship programme.