# A radio bridge connecting the minihalo and phoenix in the Abell 85 cluster

**Authors:** Ramij Raja, Majidul Rahaman, Abhirup Datta, Oleg M. Smirnov  
**arXiv:** [2308.09005](https://arxiv.org/abs/2308.09005)  
**Date:** 2023-08-17  
**Summary page:** https://www.summarizepaper.com/en/paper/2308.09005v1/

## Key points

- Abell 85 galaxy cluster located at nodes of cosmic filaments, exhibits significant hydrodynamical activity
- Unusual case where cool core coexists with multiple ongoing merging processes
- Presence of minihalo in center of Abell 85 confirmed using uGMRT and MeerKAT L-band instruments
- Discovery of radio bridge connecting central minihalo to peripheral radio phoenix within Abell 85, spanning 220 kpc with mean surface brightness of $0.14\ \mu$Jy/arcsec$^2$
- Flux density around 4.88 mJy at 700 MHz, spectral index calculated as $\alpha_{700}^{1.28} = -0.92$
- Proposed mechanisms for generating radio bridge include turbulent re-acceleration induced by gas dynamics and merging shocks
- Study sheds light on complex dynamics within galaxy clusters like Abell 85, challenging existing astrophysical models and providing insights into galaxy cluster evolution

## Summary

The study titled "A radio bridge connecting the minihalo and phoenix in the Abell 85 cluster" by Ramij Raja, Majidul Rahaman, Abhirup Datta, and Oleg M. Smirnov delves into the unique characteristics of the Abell 85 galaxy cluster. This cluster is located at the nodes of cosmic filaments and exhibits significant hydrodynamical activity. While cool core clusters are typically considered to be relatively relaxed systems with minimal merging activity, Abell 85 stands out as an exceptional case where a cool core coexists with multiple ongoing merging processes. Using observations from the 700 MHz uGMRT and MeerKAT L-band instruments as part of the MGCLS project, the researchers confirmed the presence of a minihalo in the center of Abell 85 at 700MHz. This minihalo was recently discovered within MGCLS data. Additionally, they made a novel discovery of a radio bridge that connects the central minihalo to a peripheral radio phoenix within Abell 85. The radio bridge spans about 220 kpc in size and exhibits a mean surface brightness of approximately $0.14\ \mu$Jy/arcsec$^2$, with a flux density of around 4.88 mJy at 700 MHz. Its spectral index is calculated to be $\alpha_{700}^{1.28} = -0.92$. While there are uncertainties regarding the origin of seed relativistic electrons, it is proposed that turbulent re-acceleration mechanisms induced by both spiraling sloshing gas in the intracluster medium (ICM) and post-shock turbulence from outgoing merging shocks associated with phoenix formation could be responsible for generating this intriguing radio bridge phenomenon. This comprehensive study sheds light on the complex dynamics within galaxy clusters like Abell 85, highlighting how seemingly relaxed systems can still exhibit intricate interactions and structures that challenge existing astrophysical models. The findings contribute valuable insights into our understanding of galaxy cluster evolution and provide new avenues for further research into the mechanisms driving such phenomena in cosmic environments.