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Revisiting the giant radio galaxy ESO 422-G028 - I. Discovery of a neutral inflow and recent star formation in a restarted giant

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 Wide-Field Spectrograph (WiFeS). 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 $10^{7.6}\, \rm M_\odot$ that is predominantly located in the north-west region of the galaxy. Unusually, the ionized gas kinematics reveal two distinct discs 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 ionized gas discs 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 active galactic nucleus (AGN) activity.
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Submitted on : Monday, May 2, 2022 - 2:55:21 PM
Last modification on : Thursday, May 12, 2022 - 6:22:03 PM

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Henry R. M. Zovaro, Chris J. Riseley, Philip Taylor, Nicole P. H. Nesvadba, Tim J. Galvin, et al.. Revisiting the giant radio galaxy ESO 422-G028 - I. Discovery of a neutral inflow and recent star formation in a restarted giant. Monthly Notices of the Royal Astronomical Society, Oxford University Press (OUP): Policy P - Oxford Open Option A, 2022, 509, pp.4997-5017. ⟨10.1093/mnras/stab3140⟩. ⟨insu-03656925⟩

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