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

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

Abstract

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.

Citation

Walmsley, M., Lintott, C., Géron, T., Kruk, S., Krawczyk, C., Willett, K. W., Bamford, S., Kelvin, L. S., Fortson, L., Gal, Y., Keel, W., Masters, K. L., Mehta, V., Simmons, B. D., Smethurst, R., Smith, L., Baeten, E. M., & MacMillan, C. (2022). Galaxy Zoo DECaLS: Detailed visual morphology measurements from volunteers and deep learning for 314 000 galaxies. Monthly Notices of the Royal Astronomical Society, 509(3), 3966-3988. https://doi.org/10.1093/mnras/stab2093

• Journal Article Type: Article
• Acceptance Date: Jul 16, 2021
• Online Publication Date: Sep 30, 2021
• Publication Date: Jan 1, 2022
• Deposit Date: Jan 26, 2022
• Publicly Available Date: Jan 26, 2022
• Journal: Monthly Notices of the Royal Astronomical Society
• Print ISSN: 0035-8711
• Electronic ISSN: 1365-2966
• Publisher: Oxford University Press
• Peer Reviewed: Peer Reviewed
• Volume: 509
• Issue: 3
• Pages: 3966-3988
• DOI: https://doi.org/10.1093/mnras/stab2093
• Keywords: Space and Planetary Science; Astronomy and Astrophysics
• Public URL: https://nottingham-repository.worktribe.com/output/7340708
• Publisher URL: https://academic.oup.com/mnras/article/509/3/3966/6378289