  We use a semianalytic model of galaxy formation to compare the predictions of
two quenching scenarios: halo quenching and black-hole (BH) quenching. After
calibrating both models so that they fit the mass function of galaxies, BH
quenching is in better agreement with the fraction of passive galaxies as a
function of stellar mass $M_*$ and with the galaxy morphological distribution
on a star-formation-rate vs. $M_*$ diagram. Besides this main finding, there
are two other results from this research. First, a successful BH-quenching
model requires that minor mergers contribute to the growth of supermassive BHs.
If galaxies that reach high $M_*$ through repeated minor mergers are not
quenched, there are too many blue galaxies at high masses. Second, the growth
of BHs in mergers must become less efficient at low masses in order to
reproduce the $M_{\rm BH}$--$M_*$ relation and the passive fraction as a
function of $M_*$, in agreement with the idea that supernovae prevent efficient
BH growth in systems with low escape speeds. Our findings are consistent with a
quasar-feedback scenario in which BHs grow until they are massive enough to
blow away the cold gas in their host galaxies and to heat the hot
circumgalactic medium to such high entropy that its cooling time becomes long.
They also support the notion that quenching and maintenance correspond to
different feedback regimes.
