Galaxy Zoo: Quantitative visual morphological classifications for 48 000 galaxies from CANDELS

B. D. Simmons, Chris Lintott, Kyle W. Willett, Karen L. Masters, Jeyhan S. Kartaltepe, Boris Häußler, Sugata Kaviraj, Coleman Krawczyk, S. J. Kruk, Daniel H. McIntosh, R. J. Smethurst, Robert C. Nichol, Claudia Scarlata, Kevin Schawinski, Christopher J. Conselice, Omar Almaini, Henry C. Ferguson, Lucy Fortson, William Hartley, Dale KocevskiAnton M. Koekemoer, Alice Mortlock, Jeffrey A. Newman, Steven P. Bamford, N. A. Grogin, Ray A. Lucas, Nimish P. Hathi, Elizabeth McGrath, Michael Peth, Janine Pforr, Zachary Rizer, Stijn Wuyts, Guillermo Barro, Eric F. Bell, Marco Castellano, Tomas Dahlen, Avishai Dekel, Jamie Ownsworth, Sandra M. Faber, Steven L. Finkelstein, Adriano Fontana, Audrey Galametz, Ruth Grützbauch, David Koo, Jennifer Lotz, Bahram Mobasher, Mark Mozena, Mara Salvato, Tommy Wiklind

Research output: Contribution to journalArticlepeer-review

58 Scopus citations


We present quantified visual morphologies of approximately 48 000 galaxies observed in three Hubble Space Telescope legacy fields by the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) and classified by participants in the Galaxy Zoo project. 90 per cent of galaxies have z ≤ 3 and are observed in rest-frame optical wavelengths by CANDELS. Each galaxy received an average of 40 independent classifications, which we combine into detailed morphological information on galaxy features such as clumpiness, bar instabilities, spiral structure, and merger and tidal signatures. We apply a consensus-based classifier weighting method that preserves classifier independence while effectively downweighting significantly outlying classifications. After analysing the effect of varying image depth on reported classifications, we also provide depth-corrected classifications which both preserve the information in the deepest observations and also enable the use of classifications at comparable depths across the full survey.Comparing the Galaxy Zoo classifications to previous classifications of the same galaxies shows very good agreement; for some applications, the high number of independent classifications provided by Galaxy Zoo provides an advantage in selecting galaxies with a particular morphological profile, while in others the combination of Galaxy Zoo with other classifications is a more promising approach than using any one method alone.We combine the Galaxy Zoo classifications of 'smooth' galaxies with parametric morphologies to select a sample of featureless discs at 1 ≤ z ≤ 3, which may represent a dynamically warmer progenitor population to the settled disc galaxies seen at later epochs.

Original languageEnglish (US)
Pages (from-to)4420-4447
Number of pages28
JournalMonthly Notices of the Royal Astronomical Society
Issue number4
StatePublished - Feb 1 2017

Bibliographical note

Funding Information:
The authors wish to thank the anonymous referee for helpful comments which improved this paper. Astropy (Astropy Collaboration et al. 2013), TOPCAT (Taylor 2005), and an OS X widget form of the JavaScript Cosmology Calculator (Wright 2006; Simpson et al. 2013b) were used while preparing this paper. Fig. 5 was created using SANKEYMATIC at BDS gratefully acknowledges support from the Oxford Martin School and Balliol College, Oxford. Support for this work was provided by the National Aeronautics and Space Administration through Einstein Postdoctoral Fellowship Award 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. SJK acknowledges funding from the STFC Grant Code ST/MJ0371X/1. We thank M. 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 done. The development of Galaxy Zoo was supported in part by the Alfred P. Sloan Foundation. Galaxy Zoo was supported by The Leverhulme Trust. This work is based on observations taken by the CANDELS Multi-Cycle Treasury Program with the NASA/ESA HST, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555.

Publisher Copyright:
© 2016 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.


  • Galaxies: bulges
  • Galaxies: elliptical and lenticular, cD
  • Galaxies: general
  • Galaxies: spiral
  • Galaxies: structure
  • galaxies: evolution


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