The Supermassive Black Hole Mass - Spheroid Stellar Mass Relation for
  S\'ersic and Core-S\'ersic Galaxies
  We have examined the relationship between supermassive black hole mass
(M$_{BH}$) and the stellar mass of the host spheroid (M$_{sph,*}$) for a sample
of 75 nearby galaxies. To derive the spheroid stellar masses we used improved
2MASS K$_s$-band photometry from the ARCHANGEL photometry pipeline. Dividing
our sample into core-S\'ersic and S\'ersic galaxies, we find that they are
described by very different M$_{BH}$-M$_{sph,*}$ relations. For core-S\'ersic
galaxies - which are typically massive and luminous, with M$_{BH} \gtrsim
2x10^8 M_\odot$ - we find M$_{BH} \propto M_{sph,*}^{(0.97 \pm 0.14)}$,
consistent with other literature relations. However, for the S\'ersic galaxies
- with typically lower masses, M$_{sph,*} \lesssim 3x10^10 M_\odot$ - we find
M$_BH \propto M_{sph,*}^{(2.22 \pm 0.58)}$, a dramatically steeper slope that
differs by more than 2 standard deviations. This relation confirms that, for
S\'ersic galaxies, M$_{BH}$ is not a constant fraction of M$_{sph,*}$. S\'ersic
galaxies can grow via the accretion of gas which fuels both star formation and
the central black hole, as well as through merging. Their black hole grows
significantly more rapidly than their host spheroid, prior to growth by dry
merging events that produce core-S\'ersic galaxies, where the black hole and
spheroid grow in lock step. We have additionally compared our S\'ersic
M$_{BH}$-M$_{sph,*}$ relation with the corresponding relation for nuclear star
clusters, confirming that the two classes of central massive object follow
significantly different scaling relations.
