Galaxy Zoo: An independent look at the evolution of the bar fraction
  over the last eight billion years from HST-COSMOS
  We measure the redshift evolution of the bar fraction in a sample of 2380
visually selected disc galaxies found in Cosmic Evolution Survey (COSMOS)
Hubble Space Telescope (HST) images. The visual classifications used to
identify both the disc sample and to indicate the presence of stellar bars were
provided by citizen scientists via the Galaxy Zoo: Hubble (GZH) project. We
find that the overall bar fraction decreases by a factor of two, from 22+/-5%
at z=0.4 (tlb = 4.2 Gyr) to 11+/-2% at z=1.0 (tlb = 7.8 Gyr), consistent with
previous analysis. We show that this decrease, of the strong bar fraction in a
volume limited sample of massive disc galaxies [stellar mass limit of
log(Mstar/Msun) > 10.0], cannot be due to redshift dependent biases hiding
either bars or disc galaxies at higher redshifts. Splitting our sample into
three bins of mass we find that the decrease in bar fraction is most prominent
in the highest mass bin, while the lower mass discs in our sample show a more
modest evolution. We also include a sample of 98 red disc galaxies. These
galaxies have a high bar fraction (45+/-5%), and are missing from other COSMOS
samples which used SED fitting or colours to identify high redshift discs. Our
results are consistent with a picture in which the evolution of massive disc
galaxies begins to be affected by slow (secular) internal process at z~1. We
discuss possible connections of the decrease in bar fraction to the redshift,
including the growth of stable disc galaxies, mass evolution of the gas content
in disc galaxies, as well as the mass dependent effects of tidal interactions.
