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The Milky Way’s Vestigial Nuclear Jet: Traced with Molecules and X-rays, Modeled with Simulations

Presentation #115.01 in the session The Milky Way: Galactic Center and Outflows.

Published onJun 29, 2022
The Milky Way’s Vestigial Nuclear Jet: Traced with Molecules and X-rays, Modeled with Simulations

There is evidence from residual, non-stellar ionization at various distances that the Galactic Center is recovering from power surges up to Seyfert intensity within the last few Myr. Nuclear jets extending to kpc scale are occasional features in barred-spiral Seyferts (e.g., NGC 1068) and are presumably intermittent as their gas supplies are modulated. We interpret multi-wavelength observations of Milky Way structures that are consistent with the influence of a faded nuclear jet out to 2.1 arcmin (5 pc) from the Galactic Center, and up to 300 pc in our simulations. We earlier reported that Chandra X-ray protrusion G359.944-0.052 along PA 125° at 12-21 arcsec radius (a previously proposed jet candidate) is opposed diametrically across Sgr A* by a linear molecular flow. Archival ALMA spectra traced the flow out to 1.4 arcmin radius and over 20 km/s extent centered at +80 km/s in CS(J=2-1) and CH3OH(J=2-1) but not e.g., SiO. Our new ALMA CS(J=2-1) and (J=3-2) spectra now trace this flow to 2.1 arcmin radius at 2 arcsec resolution, their flux ratio indicating n(H2) ~104.5 cm-3 and LTE gas mass ~1200 (Tex/200 K) MΘ. CH3OH(J=3-2) spectra would constrain gas Tex hence energetics. The kinematical details of this molecular feature are consistent with mostly lateral expansion into dense gas around a now vestigial jet.

Our PLUTO and Athena++ 3D simulation suite launched modest jets of constant energy 1041-1042 erg s-1 and at various inclinations through fractal distributions of ISM clouds that form the toroidal, circumnuclear disk (CND) at 1.5 pc radius and the Galactic gas disk beyond. A more powerful jet is possible at lower duty cycle. Within the tilted CND the Western Arc of the ionized nuclear minispiral is intersected by a bi-directional jet inclined 5-30° from the Galactic polar axis to mass-load the linear X-ray feature on one side; the inclination range reflects uncertainty of the minispiral gas orbits. The over-pressure of the fading counter-jet taps the closest part of the CND to maintain the weak molecular flow. We also simulated gas flows across the 500 pc spanned by MeerKAT radio and XMM-Newton X-ray images that reach the base of the Fermi gamma-ray bubbles. As jet particles percolated through the cloud distribution for ≥0.25 Myr, gas loops and arches developed that often resemble the observed radio patterns and prominent X-ray channel. Such features are found around AGN such as NGC 1068.

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