Impact of super-massive black hole feedback on the properties of X-ray emitting gas in galaxy groups and clusters

Abstract

The multiphase gas that exists in the ambient medium of large ($\gtrsim 10^{13} \text{M}_\odot$) cosmic halos is strongly impacted by feedback from a central Active Galactic Nuclei (AGN). This gas, which makes up either the Intra-group Medium (IGrM) or Intra-cluster Medium (ICM) depending on the size of the halo, determines the evolution of the central massive galaxy and of the system as a whole, through processes such as accretion onto galaxies, ram-pressure stripping of satellites, and the transfer of energy via pressure and gravity waves. Exactly how these processes operate, and how this gas is impacted itself by powerful kinetic feedback from the central black hole, remains poorly understood. Cosmological simulations, coupled with high-resolution zoom-ins, are ideal laboratories in which to investigate the feedback cycle as a whole and make new inroads into understanding the flow of baryons, energy, and entropy in these systems.

In this thesis I have started by constructing a powerful software pipeline to create and analyse highly-realistic mock X-ray observations of simulated halos in the Simba suite. Using this package, MOXHA (which is publicly available), I have made a mock predictive Athena-IFU catalogue of the $\sim100$ most massive halos in Simba and used observer-like techniques to translate the simulation data to observation space as precisely as possible. I find good agreement in Simba with observed X-ray scaling relations, reproducing an under-luminous, overly-hot mass range below $10^{13.5} \text{M}_\odot$. This is indicative of the black hole jet feedback more easily evacuating the low-entropy gas from the centers of these potential wells, and demonstrates the feedback model's ability to provide sufficient energy and momentum flux. Furthermore I demonstrated that the inferred halo mass bias is significantly under-estimated when mass-weighting the pressure profile in simulations. My work shows that for proper comparison to observation data it is imperative to use a luminosity-weighting scheme, which I find agrees very well with a full deprojection and spectral-fitting procedure.

Motivated by some promising features I identified in several of the mock observations presented in the aforementioned study that appeared to be X-ray cavities, I decided to investigate further using higher-resolution zoom-in simulations. This work makes up the next chapter of this thesis. Using a suite of 34 zooms spanning $10^{12}-10^{13}\text{M}_\odot$ in $\text{M}_\text{500}$, I found many viable X-ray bubbles over the timescale of $700$ Myr - the first time such features have been shown to be produced ad-hoc by a modern cosmological simulation. I found that these bubbles matched the morphology of observed cavities well. I furthermore found that the relation between the derived cavity enthalpy and the bolometric cooling luminosity also shows excellent agreement, and again shows an ability for the central AGN in the Simba model to strongly heat and reduce the entropy in the centers of these halos.

This thesis ends with a discussion of my current work, which is focused on the response of cold gas in these zoom-in simulations to the inflation and subsequent evolution of AGN-inflated X-ray cavities, and to the motion of satellite galaxies. In this work I present some preliminary results showing how cold gas can be precipitated from the stirring of the IGrM/CGM by kinetic feedback from supermassive black holes. I also investigate the impact of bubbles and satellites on the $t_{cool}/t_{ff}$ ratio, which determines whether gas can fully condense in these systems.