Seeing the stormy lives of galaxy clusters via depolarization

Alvina Yee Lian On^1,2*, Jennifer Yik Ham Chan^3,4,5, Paul Chong Wa Lai^2,6, Kinwah Wu²

¹Physics Division, National Center for Theoretical Sciences, Taipei, 10617, Taiwan
²Mullard Space Science Laboratory, University College London, Surrey, RH5 6NT, UK
³Dunlap Institute for Astronomy and Astrophysics, University of Toronto, Toronto, ON M5S 3H8, Canada
⁴Faculty of Arts and Science, University of Toronto, Toronto, ON M5S 3G3, Canada
⁵Canadian Institute for Theoretical Astrophysics, University of Toronto, Toronto, ON M5S 3H8, Canada
⁶Department of Physics, University of Hong Kong, Hong Kong SAR, China

* Presenter:Alvina Yee Lian On, email:alvina.on@phys.ncts.ntu.edu.tw

It is important to understand the effects of polarization to correctly infer the magneto-ionic properties of the diffuse intracluster medium (ICM). Depolarization effects due to Faraday rotation are often significant at low radio frequencies. In particular, the observed linear polarization fraction of radio sources in the field of a merging galaxy cluster may not always truly indicate their intrinsic degrees of linear polarization. It is also possible for some sources to appear as unpolarized in an observation, even if they are intrinsically polarized. In this work, we quantify the effects on polarization of radio sources behind a large-scale intracluster shock. Our ray-tracing calculations reveal that, generally, bright sources do not experience any significant changes in polarization, whereas faint sources either get severely depolarized or repolarized as their radiation propagates through the ICM. Notably, the degree of linear polarization increases in the vicinity of the intracluster shock, where the gas and magnetic fields are highly compressed. The observed linear polarization fraction is also sensitive to the viewing angles. These effects would impact the interpretations of radio observations, particularly with BURSTT and SKA-LOW, where the polarization bias in faint sources must be corrected for in the statistical analyses of rotation measure grids.

Keywords: polarization, magnetic fields , galaxies: clusters: intracluster medium, radiative transfer, radiation mechanism: non-thermal