Supermassive black holes and their host spheroids II. The red and blue
  sequence in the $M_{\rm BH} - M_{\rm *,sph}$ diagram
  In our first paper, we performed a detailed (i.e. bulge, disks, bars, spiral
arms, rings, halo, nucleus, etc.) decomposition of 66 galaxies, with directly
measured black hole masses, $M_{BH}$, that had been imaged at $3.6~\mu m$ with
Spitzer. Our sample is the largest to date and, for the first time, the
decompositions were checked for consistency with the galaxy kinematics. We
present correlations between $M_{ BH}$ and the host spheroid (and galaxy)
luminosity, $L_{sph}$ (and $L_{gal}$), and also stellar mass, $M_{*,sph}$.
While most previous studies have used galaxy samples that were overwhelmingly
dominated by high-mass, early-type galaxies, our sample includes 17 spiral
galaxies, half of which have $M_{BH} < 10^7~M_\odot$, and allows us to better
investigate the poorly studied low-mass end of the $M_{BH} - M_{*,sph}$
correlation. The bulges of early-type galaxies follow $M_{BH} \propto
M_{*,sph}^{1.04 \pm 0.10}$ and define a tight red sequence with intrinsic
scatter $\epsilon = 0.43 \pm 0.06~dex$ and a median $M_{BH}/M_{*,sph}$ ratio of
$0.68 \pm 0.04\%$, i.e.~a $\pm 2\sigma$ range of 0.1-5%. At the low-mass end,
the bulges of late-type galaxies define a much steeper blue sequence, with
$M_{BH} \propto M_{*,sph}^{2-3}$, indicating that gas-rich processes feed the
black hole more efficiently than the host bulge as they coevolve. We
additionally report that: i) our Sersic galaxy sample follows a less steep
sequence than previously reported; ii) bulges with Sersic index $n<2$, argued
by some to be pseudo-bulges, are not offset to lower $M_{BH}$ from the
correlation defined by the current bulge sample with $n>2$; and iii) $L_{sph}$
and $L_{gal}$ correlate equally well with $M_{BH}$, in terms of intrinsic
scatter, only for early-type galaxies - once reasonable numbers of spiral
galaxies are included, the correlation with $L_{ sph}$ is better than that with
$L_{gal}$.
