Relativistic jet feedback – II. Relationship to gigahertz peak spectrum and compact steep spectrum radio galaxies

Description

Abstract Giant radio galaxies provide important clues into the life cycles and triggering mechanisms of radio jets. With large-scale jets spanning 1.8 Mpc, ESO 422–G028 (z = 0.038) is a giant radio galaxy that also exhibits signs of restarted jet activity in the form of pc-scale jets. We present a study of the spatially-resolved stellar and gas properties of ESO 422–G028 using optical integral field spectroscopy from the WiFeS spectrograph. In addition to the majority $\sim 13\, \rm Gyr$ old stellar population, ESO 422–G028 exhibits a much younger ($\lesssim 10\, \rm Myr$ old) component with an estimated mass of $10^{7.6}\, \rm M_\odot$ which is predominantly located in the North-West region of the galaxy. Unusually, the ionised gas kinematics reveal two distinct disks traced by narrow ($\sigma _{\rm H\alpha } < 100 \, \rm km\, s^{-1}$) and broad ($\sigma _{\rm H\alpha } > 150 \, \rm km\, s^{-1}$) Hα emission respectively. Both ionised gas disks are misaligned with the axis of stellar rotation, suggesting an external origin. This is consistent with the prominent interstellar Na D absorption, which traces a $1 - 3 \, \rm M_\odot \, yr^{-1}$ inflow of neutral gas from the North. We posit that an inflow of gas – either from an accretion event or a gas-rich merger – has triggered both the starburst and the restarted jet activity, and that ESO 422–G028 is potentially on the brink of an epoch of powerful AGN activity.

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