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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


Sugata Kaviraj

Coleman Krawczyk

S.J. Kruk

Daniel H. McIntosh

Rebecca J. Smethurst

Robert C. Nichol

Claudia Scarlata

Kevin Schawinski

Christopher J. Conselice

Professor of Astrophysics

Henry C. Ferguson

Lucy Fortson

William Hartley

Dale Kocevski

Anton 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


David Koo

Jennifer Lotz

Bahram Mobasher

Mark Mozena

Mara Salvato

Tommy Wiklind


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 down-weighting 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.


Simmons, B., Lintott, C., Willett, K. W., Masters, K. L., Kartaltepe, J. S., Häußler, B., …Wiklind, T. (2017). Galaxy Zoo: quantitative visual morphological classifications for 48 000 galaxies from CANDELS. Monthly Notices of the Royal Astronomical Society, 464(4),

Journal Article Type Article
Acceptance Date Oct 5, 2016
Online Publication Date Oct 18, 2016
Publication Date Feb 1, 2017
Deposit Date Jan 6, 2017
Publicly Available Date Jan 6, 2017
Journal Monthly Notices of the Royal Astronomical Society
Print ISSN 0035-8711
Electronic ISSN 0035-8711
Publisher Oxford University Press
Peer Reviewed Peer Reviewed
Volume 464
Issue 4
Keywords galaxies: bulges ; galaxies: elliptical and lenticular, cD ; galaxies: evolution ; galaxies: general ; galaxies: spiral ; galaxies: structure
Public URL
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