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

Abstract

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 GMRT 325 MHz observations failed to detect extended radio emission associated with the cluster as is typically seen in such systems. We present new, multi-configuration 1 − 2 GHz Karl G. Jansky Very Large Array (VLA) observations of Abell 2146 totalling 16 hours 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 which we classify as a radio relic and one associated with the subcluster core which 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 (P 1.4GHz, halo = 2.4 ± 0.2 × 10 23 W Hz −1 and P 1.4GHz, relic = 2.2 ± 0.2 × 10 23 W Hz −1 ). The flux measurement of the halo, as well as its morphology, also suggest 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 halos in merging clusters should be detected by future radio facilities such as the Square Kilometre Array (SKA).

Characterizing the radio emission from the binary galaxy cluster merger Abell 2146

“…We also obtained measurements at 150 MHz from the TGSS-ADR1 (Intema et al 2017), 325 MHz (Russell et al 2011), 612 MHz (see Sec. 3.2), VLA 1.5 GHz (Hlavacek-Larrondo et al 2018), and 5 GHz (Hogan et al 2015;Hlavacek-Larrondo et al 2018) observations and present the spectral properties of these sources in Fig. 2 and Table 2.…”

“…More details on the VLA observations are given in Table 1. The calibration for each configuration of the VLA data sets was performed separately in CASA by Hlavacek-Larrondo et al (2018). For a full description of the procedure, we refer to Hlavacek-Larrondo et al (2018).…”

“…Feretti et al 2004;Dasadia et al 2016), and Abell 2146 (e.g. Russell et al 2010;Hlavacek-Larrondo et al 2018). In these regions, extended radio emission is either undetected at the shocks (e.g.…”

A massive cluster at z = 0.288 caught in the process of formation: The case of Abell 959

“…; A1682, A2261, RXCJ1314.4-2515, ZwCL5247). Lastly, in the last two years, there has been a rapid increase in studies of individual or small samples of RH systems (see Bernardi et al 2016;Knowles et al 2016;Girardi et al 2016;Venturi et al 2017;Parekh et al 2017;Duchesne et al 2017;Hoang et al 2017;Wilber et al 2018;Hlavacek-Larrondo et al 2018;Cuciti et al 2018;Savini et al 2019). We have collected measurements from these studies to form a larger sample of RHs.…”

“…There are a number of halo systems that show evidence of X-ray shocks associated with the radio relic emission (e.g. A521, Bullet, A754, El Gordo, A2146; Giacintucci et al 2006Giacintucci et al , 2008Shimwell et al 2015;Macario et al 2011;Botteon et al 2016;Russell et al 2010;Hlavacek-Larrondo et al 2018). Such shocks, thought to be generated during the merger, are typically found to lie roughly perpendicular to the merger axis, often at the outskirts of the cluster.…”