Sensitive radio surveys with broad sky coverage have revealed that the local radio AGN population is dominated by sources with lower powers than those previously studied as representative of the class. High-excitation radio galaxies (HERGs) with intermediate radio powers (10^22.5 < L_{1.4GHz} < 10^25 W/Hz) represent a particularly important subset of these lower-power objects, given their strong association with kinematic disturbances in the multiphase gas of their host galaxies that can affect subsequent star formation and black hole accretion. Study of radio-intermediate HERG sources is hence important for obtaining a more representative understanding of the role of radio AGN in galaxy evolution. Despite this, little is currently known about the typical properties of such objects. High-radio-power HERGs are found to show predominantly elliptical morphological types and frequent signatures of galaxy mergers and interactions, which are thought to provide the dominant triggering mechanism for their AGN. In this talk, I will discuss how we have used deep optical imaging observations of radio-intermediate HERGs to characterise their detailed morphologies for the first time, in order to determine the dominant host types and the importance of merger-based triggering in the intermediate radio power regime. The dependence of these properties on radio power and or optical emission line luminosity has also been investigated in detail, using similar analysis of the morphologies of powerful 3CR radio galaxies and the hosts of Type 2 quasars, alongside stellar-mass- and redshift-matched non-active control galaxies. In addition, previous results suggest that high-radio-power HERGs are predominantly associated with double-lobed, edge-brightened (FRII) extended radio structures. Such radio structures are also seen (on smaller scales) for some Seyfert galaxies at low radio powers, which has led to suggestions that these structures are connected with radiatively-efficient AGN accretion at all radio powers. I will discuss how we have also used high-resolution VLA observations of radio-intermediate HERGs to test whether this connection continues at intermediate radio powers, or whether they exhibit the highly compact morphologies found from equivalent observations of LERGs with similar radio powers -- so-called "FR0s".

Location: Zoom

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