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 vi-sually selected disc galaxies found in Cosmic Evolution Survey (COSMOS) Hubble Space Telescope (HST) images. The visual classifications used both to identify the disc sample and to indicate the presence of stellar bars were provided by citizen scien-tists via the Galaxy Zoo: Hubble (GZH) project. We find that the overall bar fraction decreases by a factor of 2, 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(M?/M) ≥ 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