Galaxy Zoo DECaLS: Detailed visual morphology measurements from volunteers and deep learning for 314 000 galaxies

Mike Walmsley, Chris Lintott, Tobias Géron, Sandor Kruk, Coleman Krawczyk, Kyle W Willett, Steven Bamford, Lee S. Kelvin, Lucy Fortson, Yarin Gal, William Keel, Karen L. Masters, Vihang Mehta, Brooke D. Simmons, Rebecca Smethurst, Lewis Smith, Elisabeth M. Baeten, Christine MacMillan

Research output: Contribution to journalArticlepeer-review

63 Scopus citations


We present Galaxy Zoo DECaLS: detailed visual morphological classifications for Dark Energy Camera Legacy Survey images of galaxies within the SDSS DR8 footprint. Deeper DECaLS images (r = 23.6 versus r = 22.2 from SDSS) reveal spiral arms, weak bars, and tidal features not previously visible in SDSS imaging. To best exploit the greater depth of DECaLS images, volunteers select from a new set of answers designed to improve our sensitivity to mergers and bars. Galaxy Zoo volunteers provide 7.5 million individual classifications over 314 000 galaxies. 140 000 galaxies receive at least 30 classifications, sufficient to accurately measure detailed morphology like bars, and the remainder receive approximately 5. All classifications are used to train an ensemble of Bayesian convolutional neural networks (a state-of-the-art deep learning method) to predict posteriors for the detailed morphology of all 314 000 galaxies. We use active learning to focus our volunteer effort on the galaxies which, if labelled, would be most informative for training our ensemble. When measured against confident volunteer classifications, the trained networks are approximately 99 per cent accurate on every question. Morphology is a fundamental feature of every galaxy; our human and machine classifications are an accurate and detailed resource for understanding how galaxies evolve.

Original languageEnglish (US)
Pages (from-to)3966-3988
Number of pages23
JournalMonthly Notices of the Royal Astronomical Society
Issue number3
StatePublished - Jan 1 2022

Bibliographical note

Funding Information:
Supported by National Institutes of Health grants CA23226 and CA74131 (to N. F.), AG01751 (to P. S. R.), ES07032 (to T. J. K.), and CA 75316 (to C. C. F.). R. H. P. was supported by training grant ES07032 and the Irwin M. Arias Postdoctoral Research Fellowship from the American Liver Foundation. M. C. was supported by training grants CA09437 and GM0720 .

Publisher Copyright:
© 2021 The Author(s). Published by Oxford University Press on behalf of Royal Astronomical Society.


  • galaxies: bar
  • galaxies: general
  • galaxies: interactions
  • methods: data analysis


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