Authors: Nicholas Scott, Alister W. Graham, James Schombert
We have examined the relationship between supermassive black hole mass (MBH) and the stellar mass of the host spheroid (Msph,∗) for a sample of 75 nearby galaxies. To derive the spheroid stellar masses we used improved 2MASS Ks–band photometry from the `archangel' photometry pipeline. Dividing our sample into core-Sérsic and Sérsic galaxies, we find that they are described by very different MBH–Msph,∗ relations. For core-Sérsic galaxies — which are typically massive and luminous, with MBH > 2 x 108 MSun — we find MBH ∝ Msph,*0.97±0.14, consistent with other literature relations. However, for the Sérsic galaxies — with typically lower masses, Msph,∗ < 3 x 1010 MSun — we find MBH ∝ Msph,*2.22±0.58, a dramatically steeper slope that differs by more than 2 standard deviations. This relation confirms that, for Sérsic galaxies, MBH is not a constant fraction of Msph,∗. Sérsic 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-Sérsic galaxies, where the black hole and spheroid grow in lock step. We have additionally compared our Sérsic MBH–Msph,∗ relation with the corresponding relation for nuclear star clusters, confirming that the two classes of central massive object follow significantly different scaling relations.