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 Häußler, Anna Han, Ross Hart, Thomas Melvin, Michael Parrish, Kevin Schawinski, R. J. SmethurstArfon M. Smith

Research output: Contribution to journalArticlepeer-review

23 Scopus citations


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 (US)
Pages (from-to)4176-4203
Number of pages28
JournalMonthly Notices of the Royal Astronomical Society
Issue number4
StatePublished - Feb 1 2017

Bibliographical note

Funding Information:
KW, MG, CS, MB, and LF gratefully acknowledge support from the US National Science Foundation Grant AST1413610. Support for BDS was provided by the National Aeronautics and Space Administration through Einstein Postdoctoral FellowshipAward Number PF5-160143 issued by the Chandra X-ray Observatory Center, which is operated by the Smithsonian Astrophysical Observatory for and on behalf of the National Aeronautics Space Administration under contract NAS8-03060. KS gratefully acknowledges support from Swiss National Science Foundation Grant PP00P2_138979/1. TM acknowledges funding from the Science and Technology Facilities Council ST/J500665/1. RJS is supported by the STFC grant code ST/K502236/1. The development and hosting of Galaxy Zoo: Hubble was supported by a grant from the Alfred P. Sloan Foundation. The Zooniverse acknowledges support from a Google Global Impact Award. We thank Meg Schwamb and the ASIAA for hosting the 'Citizen Science in Astronomy' workshop, 2014 March 3-7 in Taipei, Taiwan, at which some of this analysis was initiated.We also thank Jennifer Lotz for sharing her G-M20 measurements for the AEGIS sample. We thank Coleman Krawczyk for his assistance in producing Fig. 4. We thank Nathan Cloutier and Brent Hilgart for useful discussions. We also thank the referee for thoughtful comments which improved the quality of this paper. This project made heavy use of the ASTROPY packages in PYTHON (Astropy Collaboration et al. 2013), the SEABORN plotting package (Waskom et al. 2015), astroML (Vanderplas et al. 2012), and TOPCAT (Taylor 2005, 2011). Modified code from Nick Wherry and David Schlegel was used to create the JPG images. Fig. 13 was generated with Holwerda (2005) provided valuable assistance in interpreting SEXTRACTOR output. This work is based on (GO-10134, GO-09822, GO-09425.01, GO-09583.01, GO-9500) programme observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. Funding for the SDSS and SDSS-II has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation, the US Department of Energy, the National Aeronautics and Space Administration, the Japanese Monbukagakusho, the Max Planck Society, and the Higher Education FundingCouncil for England. The SDSS website is The SDSS is managed by the Astrophysical Research Consortium for the Participating Institutions. The Participating Institutions are the American Museum of Natural History, Astrophysical Institute Potsdam, University of Basel, University of Cambridge, Case Western Reserve University, University of Chicago, Drexel University, Fermilab, the Institute for Advanced Study, the Japan Participation Group, Johns Hopkins University, the Joint Institute for Nuclear Astrophysics, the Kavli Institute for Particle Astrophysics and Cosmology, the Korean Scientist Group, the Chinese Academy of Sciences (LAMOST), Los Alamos National Laboratory, the Max-Planck-Institute for Astronomy (MPIA), the Max-Planck-Institute for Astrophysics (MPA), New Mexico State University, Ohio State University, University of Pittsburgh, University of Portsmouth, Princeton University, the United States Naval Observatory, and the University of Washington.


  • Catalogues
  • Galaxies: evolution
  • Galaxies: highredshift
  • Galaxies: structure
  • Methods: data analysis

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