Constraints on the impact of active galactic nuclei on star formation in galaxies

Abstract

Super massive black holes (SMBH) are known to reside at the centre of massive galaxies, and are visible during their growth phases as active galactic nuclei (AGN). Current theoretical models of galaxy evolution require AGN feedback processes to reproduce many of the fundamental properties of galaxies and the intergalactic medium. In an effort to constrain the effect of AGN feedback on star formation in AGN host galaxies, this thesis uses observations to test predictions from the cosmological simulations. I present ALMA and integral field unit (IFU) observations of AGN host galaxies to trace obscured and unobscured star formation as well as ionised gas kinematics.
Using deep ALMA continuum observations and multi-wavelength photometry I estimate specific star formation rate distributions of 81 X-ray AGN at z=1.5--3.2 with AGN luminosities of -- ergs s. Comparison of the observations with predictions from the EAGLE cosmological simulations shows that AGN feedback is responsible for broadening the sSFR distribution of both active and inactive galaxies by suppressing their star formation.
In the second scientific experiment, I present IFU and ALMA observations of eight X-ray AGN at z=1.4--2.6 with AGN luminosities of -- ergs s to investigate the connection between AGN driven ionised outflows and star formation. Using these observations, I conclude that star formation in AGN host galaxies is not instantly suppressed by AGN driven outflows, consistent with the global conclusions from my earlier study. I reach this conclusion whenever I use obscured or unobscured star formation tracer. Furthermore, I conclude that it is necessary to use H emission with caution when using it to trace star formation in AGN host galaxies.
In the last scientific experiment, I investigate star formation in three quasars at z2.5 that were previously presented in the literature as having evidence for suppressed star-formation at the location of ionised outflows. Using new ALMA band 7 continuum observations and re-analysing the existing archival H observations, I do not observe any suppression of star formation in these quasars.
Based on the evidence from all of my studies, I conclude that AGN feedback does not instantly suppress star formation on a global scale, but rather the feedback may have an impact seen on smaller spatial scales ( 4 kpc), or on longer timescales than a single AGN episode.