Misaligned jets from Sgr A$^*$ and the origin of Fermi/eROSITA bubbles

TL;DR

This paper investigates the origin of Fermi/eROSITA bubbles through hydrodynamical simulations of tilted jets from Sgr A*, finding that powerful jets can produce observed symmetries but conflict with line ratio observations, suggesting alternative low-luminosity sources.

Contribution

The study introduces hydrodynamical simulations of misaligned jets from Sgr A* and assesses their viability in explaining the Fermi/eROSITA bubbles, highlighting the limitations of high-power jets.

Findings

Powerful super-Eddington jets can produce symmetric bubbles but conflict with line ratios.

Low-luminosity magnetically dominated jets or winds are more consistent with observations.

Jets active for less than 6 kyr can generate the observed bubble morphology.

Abstract

One of the leading explanations for the origin of Fermi Bubbles is a past jet activity in the Galactic center supermassive black hole Sgr A$^*$. The claimed jets are often assumed to be perpendicular to the Galactic plane. Motivated by the orientation of pc-scale nuclear stellar disk and gas streams, and a low inclination of the accretion disk around Sgr A$^*$ inferred by the Event Horizon Telescope, we perform hydrodynamical simulations of nuclear jets significantly tilted relative to the Galactic rotation axis. The observed axisymmetry and hemisymmetry (north-south symmetry) of Fermi/eROSITA bubbles (FEBs) due to quasi-steady jets in Sgr A$^*$ can be produced if the jet had a super-Eddington power ($\gtrsim 5\times 10^{44}$ erg s$^{-1}$) for a short time (jet active period $\lesssim 6$ kyr) for a reasonable jet opening angle ($\lesssim 10^\circ$). Such powerful explosions are, however, incompatible with the observed O VIII/O VII line ratio towards the bubbles, even after considering electron-proton temperature non-equilibrium. We argue that the only remaining options for producing FEBs are i) a low-luminosity ($\approx 10^{40.5-41}$ erg s$^{-1}$)) magnetically dominated jet or accretion wind from the Sgr A$^*$, and ii) a SNe or TDE driven wind of a similar luminosity from the Galactic center.