The relationship between black hole mass and galaxy properties:
  Examining the black hole feedback model in IllustrisTNG
  Supermassive black hole feedback is thought to be responsible for the lack of
star formation, or quiescence, in a significant fraction of galaxies. We
explore how observable correlations between the specific star formation rate
(sSFR), stellar mass (M$_{\rm{star}}$), and black hole mass (M$_{\rm{BH}}$) are
sensitive to the physics of black hole feedback in a galaxy formation model. We
use the IllustrisTNG simulation suite, specifically the TNG100 simulation and
ten model variations that alter the parameters of the black hole model.
Focusing on central galaxies at $z = 0$ with M$_{\rm{star}} > 10^{10}$
M$_{\odot}$, we find that the sSFR of galaxies in IllustrisTNG decreases once
the energy from black hole kinetic winds at low accretion rates becomes larger
than the gravitational binding energy of gas within the galaxy stellar radius.
This occurs at a particular M$_{\rm{BH}}$ threshold above which galaxies are
found to sharply transition from being mostly star-forming to mostly quiescent.
As a result of this behavior, the fraction of quiescent galaxies as a function
of M$_{\rm{star}}$ is sensitive to both the normalization of the
M$_{\rm{BH}}$-M$_{\rm{star}}$ relation and the M$_{\rm{BH}}$ threshold for
quiescence in IllustrisTNG. Finally, we compare these model results to
observations of 91 central galaxies with dynamical M$_{\rm{BH}}$ measurements
with the caveat that this sample is not representative of the whole galaxy
population. While IllustrisTNG reproduces the observed trend that quiescent
galaxies host more massive black holes, the observations exhibit a broader
scatter in M$_{\rm{BH}}$ at a given M$_{\rm{star}}$ and show a smoother decline
in sSFR with M$_{\rm{BH}}$.
