Black Hole Mass Scaling Relations for Spiral Galaxies. II. M BH-M ∗,tot and M BH-M ∗,disk

Black hole mass (M-BH) scaling relations are typically derived using the properties of a galaxy's bulge and samples dominated by (high-mass) early-type galaxies. Studying late-type galaxies should provide greater insight into the mutual growth of black holes and galaxies in more gas-rich environments. We have used 40 spiral galaxies to establish how M-BH scales with both the total stellar mass (M-*,M-tot) and the disk's stellar mass, having measured the spheroid (bulge) stellar mass (M-*,M-sph) and presented the M-BH-M-*,(sph) relation in Paper I. The relation involving M-*,M-tot may be beneficial for estimating M-BH either from pipeline data or at higher redshift, conditions that are not ideal for the accurate isolation of the bulge. A symmetric Bayesian analysis finds log(M-BH/M-circle dot) = (3.05(-0.49)(+0.57))log {M-*,M-tot/[v(6.37 x 10(10) M-circle dot)]} + (7.25(-0.14)(+0.13)). The scatter from the regression of M-BH on M-*,M-tot is 0.66 dex; compare 0.56 dex for M-BH on M-*,M-sph and 0.57 dex for M-BH on sigma(*). The slope is > 2 times that obtained using core-Sersic early-type galaxies, echoing a similar result involving M-*,M-sph, and supporting a varied growth mechanism among different morphological types. This steeper relation has consequences for galaxy/black hole formation theories, simulations, and predicting black hole masses. We caution that (i) an M-BH-M-*,M-tot relation built from a mixture of early- and late-type galaxies will find an arbitrary slope of approximately 1-3, with no physical meaning beyond one's sample selection, and (ii) evolutionary studies of the M-BH-M-*,M-tot relation need to be mindful of the galaxy types included at each epoch. We additionally update the M-*,M-tot-(face-on spiral arm pitch angle) relation.