AGN jet-inflated bubbles as possible origin of odd radio circles

TL;DR

This study uses 3D simulations to propose that AGN jet-inflated bubbles, especially CRp-dominated ones, can explain the size, shape, and radio features of odd radio circles observed in galaxy halos.

Contribution

It introduces a novel simulation-based model showing CRp-dominated AGN jets can produce ORC-like bubbles matching observations.

Findings

CRp-dominated jets inflate large, oblate bubbles consistent with ORCs.

Longer-duration, lower-power jets create larger bubbles with edge-brightened morphology.

Efficient hadronic collisions explain the edge-brightening of ORCs.

Abstract

Odd radio circles (ORCs) are newly discovered extragalactic radio objects with unknown origin. In this work, we carry out three-dimensional cosmic-ray (CR) magnetohydrodynamic simulations using the FLASH code and predict the radio morphology of end-on active galactic nucleus (AGN) jet-inflated bubbles considering hadronic emission. We consider CR proton (CRp)-dominated jets as they tend to inflate oblate bubbles, promising to reproduce the large inferred sizes of the ORCs when viewed end-on. We find that powerful and long-duration CRp-dominated jets can create bubbles with similar sizes ($\sim 300-600$ kpc) and radio morphology (circular and edge-brightened) to the observed ORCs in low-mass ($M_{\rm vir}\sim 8\times 10^{12} - 8\times 10^{13}~M_\odot$) halos. Given the same amount of input jet energy, longer-duration (thus lower-power) jets tend to create larger bubbles since high-power jets generate strong shocks that carry away a significant portion of the jet energy. The edge-brightened feature of the observed ORCs is naturally reproduced due to efficient hadronic collisions at the interface between the bubbles and the ambient medium. We further discuss the radio luminosity, X-ray detectability, and the possible origin of such strong AGN jets in the context of galaxy evolution. We conclude that end-on CR-dominated AGN bubbles could be a plausible scenario for the formation of ORCs.