Authors: Benjamin Davis, Alister W. Graham, Ewan Cameron
The (black hole mass, MBH)–(bulge stellar mass, M*,sph) relation is, obviously, derived using two quantities. We endeavor to provide accurate values for the latter by generating detailed multi-component galaxy decompositions for the current full sample of 43 spiral galaxies having directly measured supermassive black hole masses — 35 of these galaxies have been alleged to contain pseudobulges, and another three appear bulgeless. This more than doubles the previous sample size of spiral galaxies with a finessed image analysis. We have analyzed their near-infrared images with meticulous care, accounting for not only the bulge, disk (exponential, truncated, or inclined), and bar, but also for spiral arms and rings, and additional central components (active galactic nuclei, etc.), all of which can bias the bulge parameters if they are not included. A symmetric Bayesian analysis finds MBH∝M*,sph2.44±0.31. This result corroborates previous observational studies, and simulations, which have reported a near-quadratic slope at the low-mass end of the MBH–M*,sph diagram. The non-linear slope additionally rules out the idea that many mergers, coupled with the central limit theorem, independently produced this scaling relation, and it has important implications for the formation pathway of supermassive black holes. Models that have invoked active galactic nuclei feedback to establish a linear MBH–M*,sph relation need revisiting. We additionally present an updated MBH–(Sérsic index, nsph) relation for spiral galaxy bulges, with a comparable level of scatter, and a new M*,sph–(spiral arm pitch angle, φ) relation.