Quantifying the AGN-driven ionised outflows in local Ultra-luminous Infrared Galaxies

Active-Galactic-Nuclei(AGN)-driven outflows are now routinely incorporated into models of major gas-rich mergers, as a mechanism for regulating galaxy growth. This is required to reproduce the correct observables (e.g. M-sigma relation) in such simulations. Despite this, the true importance of the AGN-driven outflows remains controversial from an observational perspective. In particular, the properties of these outflows - such as the radii, densities, mass outflow rates and coupling efficiencies - have proven challenging to quantify, and previous estimates vary over many orders of magnitude. Here, high-resolution imaging and wide-spectral-coverage spectroscopy has been used to accurately quantify the warm outflows in a sample of 9 local (z < 0.175) Ultra Luminous Infrared Galaxies (ULIRGs). These objects, which represent the most rapidly-evolving galaxies in the local Universe, are expected to contain particularly powerful outflows, and provide key targets for studying AGN-driven outflows in detail. Using [OIII] emission lines, the near-nuclear outflows are shown to be compact (0.05 < R < 6 kpc, median ~0.8 kpc), and, using trans-auroral [OII] and [SII] emission lines, they are shown to have relatively high densities (300 < n < 18000 cm^-3, median ~ 2000 cm^-3. In addition, the mass outflow rates (0.1 < M_dot < 20 M_sun/yr, median ~ 2 M_sun/yr), and coupling efficiencies (0.03 < E_dot/L_AGN < 2.5%, median ~ 0.4%), are relatively modest compared with those required by most simulations. Even under optimistic assumptions, these are only consistent with theoretical expectations if a relatively modest fraction (~10%) of the energy initially transferred by the AGN is transmitted to the warm outflows. Furthermore, the more extended (R > 5 kpc) low-surface-brightness emission-line regions seen in 60% of a more extended sample of local ULIRGs have been shown to contribute little to the total outflow powers. Overall, this thesis contributes some of the most accurately derived properties for the warm outflows in local AGN, and provides observational results which can be used for testing the merger models.