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