Speaker
Description
Blue low-excitation radio galaxies (BLERGs) may expose a missing evolutionary axis in radio-AGN unification. In the canonical picture, low-excitation radio galaxies are powered by radiatively inefficient accretion in massive, quiescent hosts, where mechanical feedback suppresses cooling and star formation. BLERGs break this expectation: they retain ongoing star formation and substantial cold-gas reservoirs while already hosting radio activity. They therefore provide a rare test of whether radio-AGN diversity reflects only accretion mode and orientation, or whether some systems are caught during a short-lived transition into maintenance-mode feedback. We present new Gemini/GNIRS near-infrared spectroscopy of eight low-redshift (z<0.1) BLERGs, combined with Pan-STARRS optical morphologies and VLASS radio continuum imaging, to investigate the origin of warm molecular gas excitation and the evolutionary state of their radio activity. We detect warm H$_2$ emission with characteristic excitation temperatures of T~2000-4000 K and luminosities comparable to those of radio-emitting early-type galaxies. However, the H$_2$ emission shows no clear positive dependence on radio power. Instead, the strongest H$_2$ emission occurs in morphologically disturbed systems, while VLASS imaging reveals compact and small-scale radio morphologies (<20 kpc) consistent with young, localized, or recently restarted jets. These results suggest that BLERGs occupy a phase in which merger-driven gas inflows and early-stage mechanical feedback coexist before radio feedback has fully coupled to the host halo leading to quiescence. In this framework, BLERGs are not merely outliers within the radio-galaxy AGN population, but possible precursors to classical maintenance-mode systems. They provide a low-redshift laboratory for testing how radio-AGN unification must be extended to include gas supply, host-galaxy evolution, and local environment. Future Roman and Euclid spectroscopy, combined with deep radio continuum imaging, will enable statistically significant BLERG samples across cosmic time, testing how compact jets, cold gas, and environment shape the emergence of radio-mode feedback.