Discovery of a Powerful >10^61 erg AGN Outburst in Distant Galaxy Cluster SPT-CLJ0528-5300 (1911.12828v1)

Abstract: We present ~103 ks of Chandra observations of the galaxy cluster SPT-CLJ0528-5300 (SPT0528, z=0.768). This cluster harbors the most radio-loud (L_1.4GHz = 1.01 x 10^33 erg/s/Hz) central AGN of any cluster in the South Pole Telescope (SPT) SZ survey with available X-ray data. We find evidence of AGN-inflated cavities in the X-ray emission, which are consistent with the orientation of the jet direction revealed by ATCA radio data. The combined probability that two such depressions -- each at ~1.4-1.8sigma significance, oriented ~180 degrees apart and aligned with the jet axis -- would occur by chance is 0.1%. At >10^61 erg, the outburst in SPT0528 is among the most energetic known in the universe, and certainly the most powerful known at z>0.25. This work demonstrates that such powerful outbursts can be detected even in shallow X-ray exposures out to relatively high redshifts (z~0.8), providing an avenue for studying the evolution of extreme AGN feedback. The ratio of the cavity power (P_cav = 9.4+/-5.8 x 10^45 erg/s) to the cooling luminosity (L_cool = 1.5+/-0.5 x 10^44 erg/s) for SPT0528 is among the highest measured to date. If, in the future, additional systems are discovered at similar redshifts with equally high P_cav/L_cool ratios, it would imply that the feedback/cooling cycle was not as gentle at high redshifts as in the low-redshift universe.

• The paper identifies an exceptionally powerful AGN outburst using Chandra X-ray data to detect ICM cavities with energy exceeding 10^61 ergs.
• It employs cavity power and cooling luminosity measurements (P_cav/L_cool ratio) to demonstrate intense AGN feedback at a redshift of 0.768.
• The findings provide new constraints for AGN feedback models, enhancing our understanding of galaxy cluster evolution in the early universe.

Overview of "Discovery of a Powerful >10^61 erg AGN outburst in the Distant Galaxy Cluster SPT-CLJ0528-5300"

The paper by Calzadilla et al. presents the discovery of a significant active galactic nucleus (AGN) outburst in the galaxy cluster SPT-CLJ0528-5300, located at a redshift of 0.768. Using Chandra X-ray observations, the researchers find evidence of AGN-inflated cavities within the intracluster medium (ICM), indicative of a massive mechanical outburst with energy exceeding 10^61 ergs. This outburst is one of the largest known, particularly at such a high redshift, and provides valuable insights into the process of AGN feedback in galaxy clusters.

Core Findings

• AGN Outburst and Cavity Detection: The paper identifies two large X-ray cavities in the ICM of SPT-CLJ0528-5300, which align with radio emissions detected by ATCA. The cavities are resolved at 1.4–1.8σ significance and are aligned with a central radio source, suggesting a common origin from AGN jets. The outburst energy is calculated to be at the scale of several times 10^61 ergs, marking it as exceptionally powerful.
• Feedback and Cooling Cycle: The paper investigates the ratio of cavity power (P_cav = 9.4 ± 5.8 × 10^45 erg s^-1) to the cooling luminosity (L_cool = 1.5 ± 0.5 × 10^44 erg s^-1) of SPT0528's ICM. The high P_cav/L_cool ratio is among the highest known, suggesting that AGN feedback at high redshifts may involve more significant heating compared to more gently regulated processes observed at lower redshifts.

Implications and Future Outlook

The paper points to several implications for AGN feedback mechanisms:

• AGN Feedback Evolution: The detection of such a powerful outburst at a redshift of 0.768 is crucial for understanding AGN feedback's role over cosmic time. If more systems with similarly high P_cav/L_cool ratios are discovered, it could imply that the feedback and cooling processes at higher redshifts were less stable and more dynamic, contrasting with the paradigms understood from local universe observations.
• Methodology for Studying Distant Clusters: This research demonstrates the practicality of detecting impactful AGN feedback out to significant redshifts using relatively shallow X-ray exposures. This presents a method for efficiently probing the evolution of AGN feedback without the need for extensive observational resources.
• Theoretical Modelling: The findings provide valuable constraints for theoretical models that aim to simulate AGN and galaxy evolution within clusters. High-energy outbursts of the scale detected may influence models of ICM heating and the subsequent suppression of cooling flows in the formation and evolution of galaxy clusters.

Overall, the discovery of a powerful AGN outburst in SPT-CLJ0528-5300 has the potential to reshape our understanding of AGN feedback processes in the early universe and contribute to the broader astrophysical narrative concerning cluster evolution and dynamics.