Resolving Jet-Driven Feedback on Sub-kpc Scales

Abstract

Relativistic jets from active galactic nuclei are known to have a profound impact on their environment, both enhancing ('positive feedback') and inhibiting ('negative feedback') star formation under certain conditions. However, the role that these feedback processes play in shaping the properties of their host galaxies and environment remains elusive. In particular, efforts to catch feedback 'in the act' have been hampered by the spatial resolution required to resolve the jets' environment. In this thesis, I advance our understanding of jet-driven feedback by comparing hydrodynamical simulations to high angular resolution optical and near-infrared integral field spectroscopy (IFS) observations, which allow us to probe the critical sub-kpc scales necessary to bridge the gap between theory and observations. To investigate feedback processes driven by young jets, I led observational programs focusing on the local radio galaxies 4C 31.04 and UGC 05771. Both galaxies harbour young jets confined to the interstellar medium (ISM), with very long baseline interferometry (VLBI) revealing jets ~100 pc and ~10 pc in size in 4C 31.04 and UGC 05771 respectively. Using adaptive optics-assisted near-infrared IFS from Gemini/NIFS and Keck/OSIRIS, I found signatures of jet-ISM interactions at radii up to 100 times larger than the size of the jets in both galaxies, a surprising result which indicated the existence of low surface-brightness jet plasma not visible in the VLBI observations. This is consistent with contemporary hydrodynamical simulations which show that the main jet streams may become temporarily halted by dense clumps in the ISM, whilst secondary plasma streams - which have a much lower surface brightness - can percolate through channels in the ISM, reaching much larger radii. The fact that this phenomenon was observed in both galaxies suggests it may be common in young radio galaxies, and may regulate star formation by driving shocks into the ISM. To investigate jet-induced star formation, I led a study of Minkowski's Object, a peculiar star-forming dwarf galaxy located in the path of the radio jet from the galaxy NGC 541 in the nearby cluster Abell 194. I carried out an IFS study of this enigmatic object using WiFeS on the ANU 2.3 m telescope, and determined that the observed emission line ratios are consistent with star formation, with a minor contribution from non-stellar ionisation sources, and an unusually large metallicity variation within the object, the origin of which remains unclear.