Vida Saeedzadeh

Topic

Dynamics of Galaxy Evolution: Insights from Circumgalactic Medium and Supermassive Black Hole Mergers

Department of Physics and Astronomy

Date & location

• Monday, April 8, 2024
• 8:30 A.M.
• Clearihue Building, Room B017

Examining Committee

Supervisory Committee

• Dr. Arif Babul, Department of Physics and Astronomy, University of Victoria (Supervisor)
• Dr. Sara Ellison, Department of Physics and Astronomy, UVic (Member)
• Prof. Afzal Suleman, Department of Mechanical Engineering, UVic (Outside Member)

External Examiner

• Prof. Biman Nath, Astronomy and Astrophysics, Raman Research Institute

Chair of Oral Examination

• Prof. Martin Segger, Department of Art History and Visual Studies, UVic

Abstract

Galaxy groups, with their complex environments, provide a laboratory for studying a range of physical processes. These processes span from large-scale structure statistics, which constrain our theories of the evolution of the Universe, to physical processes associated with galaxy formation. The conditions and processes arising in these group environments play a crucial role in galaxy evolution. Notably, over half of the Universe’s galaxies reside within these groups, and some of the most massive galaxies known are formed within these systems. Therefore, understanding the interplay within galaxy groups is crucial for obtaining a comprehensive view of galaxy evolution. Understanding how galaxies grow and evolve in these systems requires a detailed understanding of the processes that affect the gaseous halo in which they are embedded and their interactions with other galaxies. This dissertation focuses on two main areas: (i) investigating the gas reservoir around galaxies and (ii) using dual and binary supermassive black holes (SMBHs) as tracers of galaxy mergers to study the evolution of their host galaxies in different stages of SMBHs mergers.

Using high-resolution, state-of-the-art cosmological simulations, the research presented in this dissertation examines the multiphase structure of the circumgalactic medium (CGM) surrounding the central group galaxy. My findings show that the CGM around these galaxies is multiphase with its structure heavily influenced by infalling or orbiting satellite galaxies. My investigation into the CGM’s origin and evolution identifies two primary cooling mechanisms: filamentary inflows and condensations from rapidly cooling density perturbations. While current high-resolution simulations offer valuable insights into the CGM’s multiphase structure, they only begin to uncover its complexity. Achieving a deeper understanding requires simulations of even higher resolution, which poses a significant challenge due to the computational cost of increasing resolution across the entire simulation domain. To address this, I have employed the GIZMO N-body+hydrodynamics simulation code to develop a novel model that enhances resolution specifically in the CGM area, without affecting the resolution inside galaxies. This targeted approach allows for more precise and realistic modeling of the CGM’s spatial and dynamic structures while avoiding increasing the resolution in galaxies within the simulations.

In the second part of my dissertation, I delve into the dynamics of SMBH mergers, exploring the characteristics and evolution of their host galaxies during periods of active accretion and the SMBH-SMBH merger process. Leveraging the advanced SMBH model in the Romulus simulations – which accurately tracks SMBH dynamics – I compare the properties and occurrence rates of dual active galactic nuclei (AGNs) against those of single AGNs. This investigation includes examining the conditions that give rise to dual AGNs and comparing the properties of their host galaxies with those hosting single AGNs. Moreover, by creating catalogs of merging SMBHs that emit low-frequency gravitational waves, I connect studying galaxy evolution with the growing field of gravitational wave astronomy. My findings show that the binary SMBHs detectable by Pulsar Timing Arrays (PTA) predominantly reside in low-redshift, early-type galaxies, which are marked by their high stellar mass, low star formation rates, and significant halo masses. This evidence suggests that nano-Hertz gravitational wave sources are most commonly found in massive early-type galaxies situated at the centers of groups and clusters.