We present the data release for Galaxy Zoo 2 (GZ2), a citizen science project with more than 16 million morphological classifications of 304,122 galaxies drawn from the Sloan Digital Sky Survey. Morphology is a powerful probe for quantifying a galaxy's dynamical history; however, automatic classifications of morphology (either by computer analysis of images or by using other physical parameters as proxies) still have drawbacks when compared to visual inspection. The large number of images available in current surveys makes visual inspection of each galaxy impractical for individual astronomers. GZ2 uses classifications from volunteer citizen scientists to measure morphologies for all galaxies in the DR7 Legacy survey with m r > 17, in addition to deeper images from SDSS Stripe 82. While the original Galaxy Zoo project identified galaxies as early-types, late-types, or mergers, GZ2 measures finer morphological features. These include bars, bulges, and the shapes of edge-on disks, as well as quantifying the relative strengths of galactic bulges and spiral arms. This paper presents the full public data release for the project, including measures of accuracy and bias. The majority ( 90%) of GZ2 classifications agree with those made by professional astronomers, especially for morphological T-types, strong bars, and arm curvature. Both the raw and reduced data products can be obtained in electronic format at http://data.galaxyzoo.org.

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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 both to identify 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 2, from 22 ± 5% at z = 0.4 (t lb = 4.2 Gyr) to 11 ± 2% at z = 1.0 (t lb = 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 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. This publication has been made possible by the participation of more than 85,000 volunteers in the Galaxy Zoo project. Their contributions are individually acknowledged at

We use the Galaxy And Mass Assembly (GAMA) survey to measure the local Universe mass dependent merger fraction and merger rate using galaxy pairs and the CAS structural method, which identifies highly asymmetric merger candidate galaxies. Our goals are to determine which types of mergers produce highly asymmetrical galaxies, and to provide a new measurement of the local galaxy major merger rate. We examine galaxy pairs at stellar mass limits down to M * = 10 8 M ⊙ with mass ratios of <100:1 and line of sight velocity differences of ∆V < 500 km s −1 . We find a significant increase in mean asymmetries for projected separations less than the sum of the individual galaxy's Petrosian 90 radii. For systems in major merger pairs with mass ratios of <4:1 both galaxies in the pair show a strong increase in asymmetry, while in minor merger systems (with mass ratios of >4:1) the lower mass companion becomes highly asymmetric, while the larger galaxy is much less affected. The fraction of highly asymmetric paired galaxies which have a major merger companion is highest for the most massive galaxies and drops progressively with decreasing mass. We calculate that the mass dependent major merger fraction is fairly constant at ∼ 1.3 − 2% between 10 9.5 < M * < 10 11.5 M ⊙ , and increases to ∼ 4% at lower masses. When the observability time scales are taken into consideration, the major merger rate is found to approximately triple over the mass range we consider. The total co-moving volume major merger rate over the range 10 8.0 < M * < 10 11.5 M ⊙ is (1.2 ± 0.5) × 10 −3 h 3 70 Mpc −3 Gyr −1 . Key words: galaxies: general -galaxies: evolution -galaxies: interactions -galaxies: statistics ⋆ E-mail: kcasteels@gmail.com (KRVC) 2 K. R. V. Casteels et al.