Explaining the reportedly over-massive black holes in early-type
  galaxies with intermediate-scale discs
  The classification "early-type" galaxy includes both elliptically- and
lenticular-shaped galaxies. Theoretically, the spheroid-to-disc flux ratio of
an early-type galaxy can assume any positive value, but in practice studies
often consider only spheroid/disc decompositions in which the disc neatly
dominates over the spheroid at large galaxy radii, creating an inner "bulge" as
observed in most spiral galaxies. Here we show that decompositions in which the
disc remains embedded within the spheroid, labelled by some as "unphysical",
correctly reproduce both the photometric and kinematic properties of early-type
galaxies with intermediate-scale discs. Intermediate-scale discs have often
been confused with large-scale discs and incorrectly modelled as such; when
this happens, the spheroid luminosity is considerably underestimated. This has
recently led to some surprising conclusions, such as the claim that a number of
galaxies with intermediate-scale discs (Mrk 1216, NGC 1277, NGC 1271, and NGC
1332) host a central black hole whose mass is abnormally large compared to
expectations from the (underestimated) spheroid luminosity. We show that when
these galaxies are correctly modelled, they no longer appear as extreme
outliers in the (black hole mass)-(spheroid mass) diagram. This not only
nullifies the need for invoking different evolutionary scenarios for these
galaxies but it strengthens the significance of the observed (black hole
mass)-(spheroid mass) correlation and confirms its importance as a fundamental
ingredient for theoretical and semi-analytic models used to describe the
coevolution of spheroids and their central supermassive black holes.
