Extragalactic magnetism with SOFIA (Legacy Program) -- II: A magnetically-driven flow in the starburst ring of NGC 1097

TL;DR

This study uses polarized emission observations to analyze magnetic fields in NGC 1097, revealing their role in guiding gas flows towards the galaxy's center and influencing the starburst ring dynamics.

Contribution

First detailed characterization of magnetic field modes in NGC 1097's starburst ring using multi-wavelength polarization data.

Findings

Magnetic fields are concentrated at the contact regions of the outer bar and starburst ring.

Different polarization modes are observed at 89 μm and radio wavelengths, indicating distinct magnetic field structures.

Magnetic fields guide gas streams toward the galaxy's central black hole.

Abstract

Galactic bars are frequent in disk galaxies and they may support the transfer of matter towards the central engine of active nuclei. The barred galaxy NGC 1097 has magnetic forces controlling the gas flow at several kpc scales, which suggest that magnetic fields (B-fields) are dynamically important along the bar and nuclear ring. However, the effect of the B-field on the gas flows in the central kpc scale has not been characterized. Using thermal polarized emission at $89$ $\mu$m with HAWC+/SOFIA, here, we measure that the polarized flux is spatially located at the contact regions of the outer-bar with the starburst ring. The linear polarization decomposition analysis shows that the $89$ $\mu$m and radio ($3.5$ and $6.2$ cm) polarization traces two different modes, $m$, of the B-field: a constant B-field orientation and dominated by $m=0$ at $89$ $\mu$m, and a spiral B-field dominated by $m=2$ at radio. We show that the B-field at 89 $\mu$m is concentrated in the warmest region of a shock driven by the galactic-bar dynamics in the contact regions between the outer-bar with the starburst ring. Radio polarization traces a superposition of the spiral B-field outside and within the starburst ring. According to Faraday rotation measures between $3.5$ and $6.2$ cm, the radial component of the B-field along the contact regions points toward the galaxy's center on both sides. We conclude that gas streams outside and within the starburst ring follow the B-field, which feeds the black hole with matter from the host galaxy.