2018ApJ...869..113D

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_* ,tot_) and the disk's stellar mass, having measured the spheroid (bulge) stellar mass (M_* ,sph_) and presented the M_BH-M_* ,sph_ relation in Paper I. The relation involving 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_☉)=(3.05_–0.49^+0.57)log\M_* ,tot_/[υ(6.37×10¹⁰M_☉)]+(7.25_–0.14^+0.13). The scatter from the regression of M_BH on M_* ,tot_ is 0.66 dex; compare 0.56 dex for M_BH on M_* ,sph_ and 0.57 dex for M_BH on σ_*. The slope is >2 times that obtained using core-Sersic early-type galaxies, echoing a similar result involving 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_* ,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_* ,tot_ relation need to be mindful of the galaxy types included at each epoch. We additionally update the M_* ,tot_-(face-on spiral arm pitch angle) relation.