My research

CONTEXT

The cores of galaxy clusters represent the region where the interplay between different components - namely the intracluster medium (ICM), the brightest cluster galaxy (BCG) and the central active galactic nucleus (AGN) - is manifested. Multi-wavelength observations have determined that cooling of the ICM can lead to cool gas reservoirs around the BCG - albeit lower than predicted - that may fuel both star-formation and AGN activity. X-ray images of cluster cores have revealed surface brightness depressions (i.e., X-ray cavities) and weak shocks, that spatially correlate with the lobes of the central radio galaxy. The energy required to imprint such features in the ICM (in the range 10^55−10^62 erg) matches the energy released by cooling of the gas, suggesting that cluster central AGNs can prevent over-cooling of the same gas that fuels them. This finely-tuned balance is usually referred to as “AGN feeding and feedback cycle”.

OPEN QUESTIONS

Several questions on the heating-cooling regulation mechanism still remain unanswered, e.g.: (i) Is it possible to trace the feedback cycle over time? (ii) What is the role of shock heating in galaxy clusters? (iii) How are the micro AGN scales (parsec) connected to the macro environment (tens of kpc?) (iv) Can large scale ICM bulk motions (i.e., “sloshing”) disturb or even break the mechanisms that regulate feeding and feedback of the AGN?

MY PhD RESEARCH 

My PhD project aimed at answering the above questions by combining archival and proprietary multi- wavelength data. The main focus is dedicated to the galaxy cluster RBS 797, where literature studies found indications for multiple AGN outbursts in different directions, suggesting the possible presence of binary black holes (e.g., Gitti et al., 2013). Using a deep Chandra observation (420 ks awarded in Cycle 21, PI Gitti), multifrequency VLBI coverage (VLBA, EVN, and eMERLIN, PIs Gitti, Giroletti; International LOFAR stations, PI Bonafede) and recently awarded JVLA data (PI Ubertosi) of RBS 797, we have drawn a complete picture of the ICM/AGN interplay in RBS 797 over a wide range of physical scales. In parallel, my PhD aimed at clarifying the role of ICM perturbations on the stability of the feeding & feedback cycle, by studying systems with evidences of sloshing and AGN activity at the cluster center.