Galaxy Zoo: morphological classifications for 120,000 galaxies in HST legacy imaging

Kyle W. Willett, Melanie A. Galloway, Steven P. Bamford, Chris J. Lintott, Karen L. Masters, Claudia Scarlata, B. D. Simmons, Melanie Beck, Carolin N. Cardamone, Edmond Cheung, Edward M. Edmondson, Lucy F. Fortson, Roger L. Griffith, Boris Haeussler, Anna Han, Ross Hart, Thomas Melvin, Michael Parrish, Kevin Schawinski, R. J. SmethurstArfon M. Smith

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We present the data release paper for the Galaxy Zoo: Hubble (GZH) project. This is the third phase in a large effort to measure reliable, detailed morphologies of galaxies by using crowdsourced visual classifications of colour-composite images. Images in GZH were selected from various publicly released Hubble Space Telescope legacy programmes conducted with the Advanced Camera for Surveys, with filters that probe the rest-frame optical emission from galaxies out to z ∼ 1. The bulk of the sample is selected to have mI814W < 23.5, but goes as faint as mI814W < 26.8 for deep images combined over five epochs. The median redshift of the combined samples is 〈z〉 = 0.9 ± 0.6, with a tail extending out to z ≃ 4. The GZH morphological data include measurements of both bulge- and disc-dominated galaxies, details on spiral disc structure that relate to the Hubble type, bar identification, and numerous measurements of clump identification and geometry. This paper also describes a new method for calibrating morphologies for galaxies of different luminosities and at different redshifts by using artificially redshifted galaxy images as a baseline. The GZH catalogue contains both raw and calibrated morphological vote fractions for 119 849 galaxies, providing the largest data set to date suitable for large-scale studies of galaxy evolution out to z ∼ 1.
Original languageEnglish
Pages (from-to)4176-4203
Number of pages28
JournalMonthly Notices of the Royal Astronomical Society
Issue number4
Early online date8 Oct 2016
Publication statusPublished - Feb 2017


  • astro-ph.GA
  • astro-ph.CO
  • methods: data analysis
  • catalogues
  • galaxies: evolution
  • galaxies: high-redshift
  • galaxies: structure
  • RCUK
  • STFC
  • ST/J500665/1
  • ST/K502236/1


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