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Relativistic jets from active galactic nuclei may have a profound impact on their environment, both enhancing (’positive feedback’) and inhibiting (’negative feedback’) star formation under certain conditions. On cluster scales, powerful jets are believed to drive negative feedback by preventing cooling of the intracluster medium (ICM), depriving galaxies of dense gas for star formation (e.g., McNamara & Nulsen 2012). On much smaller scales, however, the role that jet-driven 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 sub-kpc spatial resolution required to resolve the jets’ environment. In this talk I will discuss my PhD research, in which I have used high-resolution optical and near-infrared integral field spectroscopy (IFS) in conjunction with state-of-the-art hydrodynamical simulations to shrink this gap in our understanding of jet-driven feedback on sub-kpc scales. To investigate feedback processes driven by young jets, I led studies of the local radio galaxies 4C 31.04 and UGC 05771. Both galaxies harbour young jets confined to the 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 AO-assisted near-IR IFS from Gemini/NIFS and Keck/OSIRIS, we found signatures of jet-ISM interactions at radii up to 100 times larger than the apparent size of the jets in both galaxies, a surprising result indicating the existence of low surface-brightness jet plasma below the detection threshold of the VLBI observations. This is consistent with contemporary hydrodynamical simulations which show that the main jet stream may become temporarily halted by a dense clump 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. To investigate jet-driven feedback in the intracluster medium, I led a study of Minkowski’s Object, a peculiar star-forming region triggered by the jet from a neighbouring galaxy. Using observations from the WiFeS spectrograph on the ANU 2.3 m telescope, we discovered a metallicity gradient across MO. We concluded that the gradient has been caused by metal-rich material entrained by the jet mixing with the pristine ICM. This is the first study of optical emission-line gas that has confirmed this phenomenon, which has previously only been observed in clusters using X-ray observations. |
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