# ALMA polarization observations of the particle accelerators in the hot spot of the radio galaxy 3C 445

## TL;DR

This study uses ALMA polarization observations at 97.5 GHz to analyze the magnetic field structure and shock processes in the hot spot of radio galaxy 3C 445, revealing complex shock and turbulence features.

## Contribution

First polarization imaging of the hot spot at millimeter wavelengths, providing new insights into magnetic fields and shock dynamics in radio galaxy hot spots.

## Key findings

- High polarization indicates shock presence.
- Disordered magnetic fields suggest turbulence.
- Evidence of multiple shock fronts and stochastic acceleration.

## Abstract

We present Atacama Large Millimeter Array (ALMA) polarization observations at 97.5 GHz of the southern hot spot of the radio galaxy 3C 445. The hot spot structure is dominated by two bright components enshrouded by diffuse emission. Both components show fractional polarization between 30 and 40 per cent, suggesting the presence of shocks. The polarized emission of the western component has a displacement of about 0.5 kpc outward with respect to the total intensity emission, and may trace the surface of a front shock. Strong polarization is observed in a thin strip marking the ridge of the hot spot structure visible from radio to optical. No significant polarization is detected in the diffuse emission between the main components, suggesting a highly disordered magnetic field likely produced by turbulence and instabilities in the downstream region that may be at the origin of the extended optical emission observed in this hot spot. The polarization properties support a scenario in which a combination of both multiple and intermittent shock fronts due to jet dithering, and spatially distributed stochastic second-order Fermi acceleration processes are present in the hot spot complex.