  We study the spiral arm morphology of a sample of the local spiral galaxies
in the Illustris simulation and explore the supermassive black hole - galaxy
connection beyond the bulge (e.g., spiral arm pitch angle, total stellar mass,
dark matter mass, and total halo mass), finding good agreement with other
theoretical studies and observational constraints. It is important to study the
properties of supermassive black holes and their host galaxies through both
observations and simulations and compare their results in order to understand
their physics and formative histories.We find that Illustris prediction for
supermassive black hole mass relative to pitch angle is in rather good
agreement with observations and that barred and non-barred galaxies follow
similar scaling relations. Our work shows that Illustris presents very tight
correlations between supermassive black hole mass and large-scale properties of
the host galaxy, not only for early-type galaxies but also low-mass, blue and
star-forming galaxies. These tight relations beyond the bulge suggest that halo
properties determine those of a disc galaxy and its supermassive black hole.
