Downstream depolarization in the Sausage relic: a 1-4 GHz Very Large Array study

G. Di Gennaro; R. J. van Weeren; L. Rudnick; M. Hoeft; M. Brüggen; D. Ryu; H. J. A. Röttgering; W. Forman; A. Stroe; T. W. Shimwell; R. P. Kraft; C. Jones; D. N. Hoang

doi:10.3847/1538-4357/abe620

paper

Downstream depolarization in the Sausage relic: a 1-4 GHz Very Large Array study

arXiv:2102.06631 · doi:10.3847/1538-4357/abe620

Abstract

Radio relics are elongated sources related to shocks driven by galaxy cluster merger events. Although these objects are highly polarized at GHz frequencies ( $≳ 20%$ ), high-resolution studies of their polarization properties are still lacking. We present the first high-resolution and high-sensitivity polarimetry study of the merging galaxy cluster CIZA J2242.8+5301 in the 1-4 GHz frequency band. We use the $Q U$ -fitting approach to model the Stokes $I$ , $Q$ and $U$ emission, obtaining best-fit intrinsic polarization fraction ( $p_{0}$ ), intrinsic polarization angle ( $χ_{0}$ ), Rotation Measure (RM) and wavelength-dependent depolarization ( $σ_{RM}$ ) maps of the cluster. Our analysis focuses on the northern relic (RN). For the first time in a radio relic, we observe a decreasing polarization fraction in the downstream region. Our findings are possibly explained by geometrical projections and/or by decreasing of the magnetic field anisotropy towards the cluster center. From the amount of depolarization of the only detected background radio galaxy, we estimate a turbulent magnetic field strength of $B_{turb} \sim 5.6 μ$ Gauss in the relic. Finally, we observe Rotation Measure fluctuations of about 30 rad m $^{- 2}$ around at the median value of 140.8 rad m $^{- 2}$ at the relic position.

arXiv comment26 pages, 23 Figures, 5 Tables. Accepted for publication in ApJ

Downstream depolarization in the Sausage relic: a 1-4 GHz Very Large Array study

Abstract

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