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Galaxy Zoo 2: detailed morphological classifications for 304 122 galaxies from the Sloan Digital Sky Survey

Research output: Contribution to journalArticle

  • Kyle W. Willett
  • Chris J. Lintott
  • Steven P. Bamford
  • Karen L. Masters
  • Brooke D. Simmons
  • Kevin R. V. Casteels
  • Edward M. Edmondson
  • Lucy F. Fortson
  • Sugata Kaviraj
  • William C. Keel
  • Thomas Melvin
  • Professor Bob Nichol
  • M. Jordan Raddick
  • Kevin Schawinski
  • Robert J. Simpson
  • Ramin A. Skibba
  • Arfon M. Smith
  • Professor Daniel Thomas
We present the data release for Galaxy Zoo 2 (GZ2), a citizen science project with more than 16 million morphological classifications of 304 122 galaxies drawn from the Sloan Digital Sky Survey (SDSS). Morphology is a powerful probe for quantifying a galaxy's dynamical history; however, automatic classifications of morphology (either by computer analysis of images or by using other physical parameters as proxies) still have drawbacks when compared to visual inspection. The large number of images available in current surveys makes visual inspection of each galaxy impractical for individual astronomers. GZ2 uses classifications from volunteer citizen scientists to measure morphologies for all galaxies in the DR7 Legacy survey with mr > 17, in addition to deeper images from SDSS Stripe 82. While the original GZ2 project identified galaxies as early-types, late-types or mergers, GZ2 measures finer morphological features. These include bars, bulges and the shapes of edge-on disks, as well as quantifying the relative strengths of galactic bulges and spiral arms. This paper presents the full public data release for the project, including measures of accuracy and bias. The majority (≳90 per cent) of GZ2 classifications agree with those made by professional astronomers, especially for morphological T-types, strong bars and arm curvature. Both the raw and reduced data products can be obtained in electronic format at
Original languageEnglish
Pages (from-to)2835-2860
JournalMonthly Notices of the Royal Astronomical Society
Issue number4
Early online date22 Sep 2013
Publication statusPublished - 11 Nov 2013


  • 2013_WillettGZ2

    Rights statement: This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2013 Royal Astronomical Society. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved

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