# Central radio galaxies in galaxy clusters: joint surveys by eROSITA and ASKAP

**Authors:** K. Böckmann, M. Brüggen, B. Koribalski, A. Veronica, T. H. Reiprich, E. Bulbul, Y. E. Bahar, F. Balzer, J. Comparat, C. Garrel, V. Ghirardini, G. Gürkan, M. Kluge, D. Leahy, A. Merloni, A. Liu, M. E. Ramos-Ceja, M. Salvato, J. Sanders, S. Shabala  
**arXiv:** [2307.13672](https://arxiv.org/abs/2307.13672)  
**Date:** 2023-07-25  
**Summary page:** https://www.summarizepaper.com/en/paper/2307.13672v1/

## Key points

- The eROSITA telescope completed the first eROSITA All-Sky Survey, detecting 10,000 galaxy clusters in the western Galactic hemisphere.
- The ASKAP telescope finished its pilot phase of the 'Evolutionary Map of the Universe' project, identifying 220,000 sources in a field that overlaps with the eROSITA survey.
- Both surveys aim to study radio-mode Active Galactic Nuclei (AGN) within clusters.
- The study examines the relationship between radio properties of brightest cluster galaxies (BCGs) and X-ray properties of their host clusters.
- Central radio sources in eRASS:1 clusters are identified or upper limits on their radio luminosity are calculated.
- Relations between X-ray properties of clusters and corresponding central radio source's properties are derived.
- A mid-infrared color criterion using WISE colors is applied to identify AGN.
- A sample of 75 clusters is investigated in total.
- There is a statistically significant correlation between X-ray luminosity of a cluster and the 944 MHz radio luminosity of its corresponding central radio galaxy.
- There is a positive trend between radio power and largest linear size (LLS) of the radio source, but no correlation with density and LLS is found.
- In high-luminosity clusters with X-ray luminosities exceeding $10^{43}$ erg s$^{-1}$, there is no longer a correlation between kinetic luminosity of radio jets and X-ray luminosity.
- An anti-correlation is found between central cooling time (t_cool) and radio luminosity (L_R), suggesting that more powerful AGN may be needed in clusters with shorter central cooling times for efficient feedback processes.

## Summary

The extended ROentgen Survey with an Imaging Telescope Array (eROSITA) telescope onboard the Spectrum-Roentgen-Gamma (SRG) mission has completed the first eROSITA All-Sky Survey (eRASS:1), which detected 10,000 galaxy clusters in the western Galactic hemisphere. Concurrently, the Australian Square Kilometre Array Pathfinder (ASKAP) telescope finished its pilot 1 phase of the 'Evolutionary Map of the Universe' (EMU) project, identifying 220,000 sources in a 270 deg$^2$ field that overlaps with eRASS:1. These surveys aim to study radio-mode Active Galactic Nuclei (AGN) within clusters. To investigate the efficiency of radio-mode feedback at the centers of galaxy clusters, this study examines the relationship between the radio properties of brightest cluster galaxies (BCGs) and the X-ray properties of their host clusters. The researchers identify central radio sources in eRASS:1 clusters or calculate upper limits on their radio luminosity. They then derive relations between the X-ray properties of these clusters and the corresponding central radio source's properties. Additionally, a mid-infrared color criterion using WISE colors is applied to identify AGN. A sample of 75 clusters is investigated in total. The results show a statistically significant correlation between the X-ray luminosity of a cluster and the 944 MHz radio luminosity of its corresponding central radio galaxy. Furthermore, there is a positive trend between the radio power and largest linear size (LLS) of the radio source. However, no correlation is found between density and LLS. Interestingly, in high-luminosity clusters with X-ray luminosities exceeding $10^{43}$ erg s$^{-1}$, there is no longer a correlation between kinetic luminosity of radio jets and X-ray luminosity. Various reasons for this observation are discussed. Additionally, an anti-correlation is found between the central cooling time (t_cool) and radio luminosity (L_R), suggesting that more powerful AGN may be needed in clusters with shorter central cooling times to maintain efficient feedback processes at their centers.