Massive Star-Forming Galaxies Have Converted Most of Their Halo Gas into
  Stars
  In the local Universe, the efficiency for converting baryonic gas into stars
is very low. In dark matter halos where galaxies form and evolve, the average
efficiency varies with galaxy stellar mass and has a maximum of about twenty
percent for Milky-Way-like galaxies. The low efficiency at higher mass is
believed to be produced by some quenching processes, such as the feedback from
active galactic nuclei. We perform an analysis of weak lensing and satellite
kinematics for SDSS central galaxies. Our results reveal that the efficiency is
much higher, more than sixty percent, for a large population of massive
star-forming galaxies around $10^{11}\ \rm M_\odot$. This suggests that these
galaxies acquired most of the gas in their halos and converted it into stars
without being affected significantly by quenching processes. This population of
galaxies is not reproduced in current galaxy formation models, indicating that
our understanding of galaxy formation is incomplete. The implications of our
results on circumgalactic media, star formation quenching and disc galaxy
rotation curves are discussed. We also examine systematic uncertainties in
halo-mass and stellar-mass measurements that might influence our results.
