Constraining the final fates of massive stars by oxygen and iron
  enrichment history in the Galaxy
  Recent observational studies of core-collapse supernovae suggest only stars
with zero-age main sequence masses smaller than $16$-$18\ M_\odot$ explode when
they are red supergiants, producing type IIP supernovae. This may imply that
more massive stars produce other types of supernovae or they simply collapse to
black holes without giving rise to bright supernovae. This failed supernova
hypothesis can lead to significantly inefficient oxygen production because
oxygen abundantly produced in inner layers of massive stars with zero-age main
sequence masses around $20$-$30\ M_\odot$ might not be ejected into the
surrounding interstellar space. We first assume an unspecified population of
oxygen injection events related to massive stars and obtain a model-independent
constraint on how much oxygen should be released in a single event and how
frequently such events should happen. We further carry out one-box galactic
chemical enrichment calculations with different mass ranges of massive stars
exploding as core-collapse supernovae. Our results suggest that the model
assuming that all massive stars with $9$-$100\ M_\odot$ explode as
core-collapse supernovae is still most appropriate in explaining the solar
abundances of oxygen and iron and their enrichment history in the Galaxy. The
oxygen mass in the Galaxy is not explained when assuming that only massive
stars with zero-age main sequence masses in the range of 9-17 $M_\odot$,
contribute to the galactic oxygen enrichment. This finding implies that a good
fraction of stars more massive than $17M_\odot$ should eject their oxygen
layers in either supernova explosions or some other mass loss processes.
