The connection between star formation and black hole growth in Active Galactic Nuclei

  • Anastasia Efthymiadou

Student thesis: Doctoral ThesisPhD


The growth of galaxies through star formation and that of the central SMBH are believed to be linked. Both require large amounts of cold gas, which when transferred to the inner kpc region of a galaxy triggers circumnuclear star formation before reaching the sub-pc region where it is accreted onto the SMBH. Thus, a tight connection between central starbursts and AGN activity is expected. Major galaxy mergers have been considered the dominant mechanism for providing the necessary gas supply and driving AGN activity for the most luminous AGN, while secular processes have been associated to less luminous AGN. In this thesis we investigate the star formation histories of the host galaxies of luminous broad-line AGN to determine the connection between star formation and AGN activity. We use 19 novel spectral components in MCMC sampling to decompose the active galaxy spectrum into the pure AGN and the host galaxy spectrum. For the merger case, we select AGN at z ∼ 0.3 with neighbouring galaxies at projected separations up to 1 Mpc to assess the influence of galaxy interactions on the SMBH growth and star formation of the host galaxies. The AGN reside in star forming hosts regardless of separation supporting the star formation - AGN activity connection, but star formation is not caused by ongoing galaxy interactions. The luminosity and spectral shape of the pure AGN spectrum is independent of proximity of neighbour indicating an absence of a merger-AGN connection. We then study the star formation histories of a large sample of AGN hosts as a function of AGN properties (black hole mass, Eddington ratio and bolometric luminosity). We find that all AGN hosts are star forming and show higher specific star formation rates with increasing bolometric luminosity.
Date of Award28 Apr 2021
Original languageEnglish
Awarding Institution
  • University of Bath
SupervisorCarolin Villforth (Supervisor) & Carole Mundell (Supervisor)


  • star formation
  • AGN
  • Supermassive black hole
  • galaxy mergers

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