Energetic Galaxy-Wide Outflows in High-z ULIRGs Hosting AGN Activity

Abstract

In this chapter we aim to address the question: can high-redshift AGN drive galaxy-wide outflows of ionised gas in the absence of extremely powerful radio jets? Most theoretical models of galaxy evolution predict that this must be the case. We investigate eight $z=1.4$–3.4 ultra-luminous infrared galaxies (ULIRGs) that host active galactic nuclei (AGN) activity, including known sub-millimetre luminous galaxies (SMGs). The targets have radio luminosities that are typical of high-redshift ULIRGs ($L_{1.4~\mathrm {GHz}}=10^{24}$–10$^{25}$ W Hz$^{-1}$) and therefore are not radio-loud AGN and do not host extremely powerful radio jets. We present integral-field spectroscopy observations, covering the [O iii]$\lambda \lambda 4959{,}5007$ emission-line doublet. We de-couple kinematic components due to the galaxy dynamics and mergers from those due to outflows. The four systems with the most powerful AGN host the signatures of large-scale energetic outflows, that is, extremely broad [O iii] emission-line profiles (FWHM ${\approx }$ 700–1400 km s$^{-1}$) across $\approx$ 4–15 kpc (i.e., across the extent of the host galaxies). The four less powerful AGN display weaker evidence for spatially extended outflows; however, this may be due, in-part, to the lower quality data for these objects. We estimate that the outflows are depositing energy into the gas in their host galaxies at considerable rates (i.e., $\dot{E}{\approx } 10^{43}$–10$^{45}$ erg s$^{-1}$). Based on the measured maximum velocities ($v_\mathrm{{max}}{\approx }$ 400–1400 km s$^{-1}$) we find that a large fraction of the gas is likely to become unbound from their host galaxies, but it is unlikely to be completely removed from the galaxy haloes. We show that the power of the growing black holes in these objects (i.e., the AGN activity) is likely to be the dominant power source for driving the outflows; however, star formation may also play a role in some of the sources.