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Galaxy Zoo: the fraction of merging galaxies in the SDSS and their morphologies

Research output: Contribution to journalArticle

  • Daniel W. Darg
  • Sugata Kaviraj
  • Chris J. Lintott
  • Kevin Schawinski
  • Marc Sarzi
  • Steven P. Bamford
  • Joseph Silk
  • Richard Proctor
  • Dan Andreescu
  • Phil Murray
  • Professor Bob Nichol
  • M. Jordan Raddick
  • Anze Slosar
  • Alexander S. Szalay
  • Professor Daniel Thomas
  • Jan Vandenberg
We present the largest, most homogeneous catalogue of merging galaxies in the nearby Universe obtained through the Galaxy Zoo project – an interface on the World Wide Web enabling large-scale morphological classification of galaxies through visual inspection of images from the Sloan Digital Sky Survey (SDSS). The method converts a set of visually inspected classifications for each galaxy into a single parameter (the ‘weighted-merger-vote fraction,’fm) which describes our confidence that the system is part of an ongoing merger. We describe how fm is used to create a catalogue of 3003 visually selected pairs of merging galaxies from the SDSS in the redshift range 0.005 < z < 0.1. We use our merger sample and values of fm applied to the SDSS Main Galaxy Spectral sample to estimate that the fraction of volume-limited (Mr < −20.55) major mergers (1/3 < M*1/M*2 < 3) in the nearby Universe is 1–3 ×C per cent, where C∼ 1.5 is a correction factor for spectroscopic incompleteness. Having visually classified the morphologies of the constituent galaxies in our mergers, we find that the spiral-to-elliptical ratio of galaxies in mergers is higher by a factor of ∼2 relative to the global population. In a companion paper, we examine the internal properties of these merging galaxies and conclude that this high spiral-to-elliptical ratio in mergers is due to a longer time-scale over which mergers with spirals are detectable compared to mergers with ellipticals.
Original languageEnglish
Pages (from-to)1043-1056
JournalMonthly Notices of the Royal Astronomical Society
Issue number2
Early online date11 Jan 2010
Publication statusPublished - 2010


  • 1043.full

    Rights statement: © 2009 The Authors. Journal compilation © 2009 RAS

    Final published version, 1.03 MB, PDF document

    Licence: CC BY-SA

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