Ionization Structure and Metal Enrichment of the Galactic Center Minispiral Observed with JWST

TL;DR

This study uses JWST/MIRI data to analyze the ionization structure and metal enrichment of the Galactic Center Minispiral, revealing detailed gas morphology, kinematics, and metallicity, and suggesting additional ionizing sources.

Contribution

First detailed mid-infrared spectroscopic analysis of the Galactic Center Minispiral revealing its ionization, metallicity, and kinematic properties with implications for local ionizing sources.

Findings

Minispiral gas metallicity is approximately 1-2.5 times solar.

Compact gas structures exhibit high-velocity blue-shifted motions.

Evidence of additional hard ionizing radiation likely from shocks or outflows.

Abstract

Sgr A* is the nearest quiescent supermassive black hole, and its proximity offers a unique opportunity to study its surrounding fuel supply. We leverage extensive spatial and spectroscopic information provided by the \jwst/MIRI MRS instrument to disentangle mid-infrared ionized gas structures in the central 0.1 parsec of the Galaxy. The Galactic Minispiral's Bar and Northern Arm are revealed by their distinct morphological and kinematic signatures. Several compact ($<1$\arcsec) gas structures including X7 also appear within $\sim 0.05$ parsec of Sgr A* in the plane of the sky, moving with blue-shifted radial velocities $\gtrsim 600$ km/s. Fine structure line measurements spanning ionization energies $\sim 7 - 55$ eV are used to constrain the incident radiation field, metal abundances (neon, argon, sulfur, nickel, and iron), and dust depletion/destruction for each identified gas structure. Overall, the Minispiral gas metallicity is $\sim 1-2.5~Z_\sun$, with a Wolf-Rayet star-driven ionizing radiation field, and significant nickel and iron dust destruction. Increased flux at energies $\gtrsim 41$ eV suggests that the compact gas structures experience an additional harder ionizing radiation source, which is most likely driven by localized fast radiative shocks from stellar winds, a hypothetical Sgr A* outflow, and/or interactions with the ambient medium.