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

By D. Darg, S. Kaviraj, Chris J. Lintott, Kevin Schawinski, M. Sarzi, Steven Bamford, J. Silk, R. Proctor, Dan Andreescu, P. Murray and 6 more. 2009

160 citations recorded by the source corpus.

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.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/5f876605a4e72bddcfb0e7bc033c9fad963a8b4b

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Citations in the corpus

Rotation-invariant convolutional neural networks for galaxy morphology prediction (2015, background): “…have already been used in a wide variety of studies on galaxy structure, formation and evolution (Bamford et al. 2009; Lintott et al. 2009; Schawinski et al. 2009; Skibba et al. 2009; Darg et al. 2010; Masters et al. 2010, 2011; Simmons et al. 2013; Melvin et al. 2014; Willett et al. 2015).”
The green valley is a red herring: Galaxy Zoo reveals two evolutionary pathways towards quenching of star formation in early-and late-type galaxies (2014, background): “…2009a; Masters et al. 2010b) and about the link between galaxy evolution and environment (e.g. Bamford et al. 2009; Skibba et al. 2009), mergers (Darg et al. 2010a, b; Kaviraj et al. 2012; Teng et al. 2012), unusual galaxy types (Cardamone et al. 2009; Lintott et al. 2009; Keel et al. 2012) and…”
Galaxy Zoo 1: data release of morphological classifications for nearly 900 000 galaxies (2010, methodology): “Darg et al. (2010a), in their study of merging galaxies, found that all galaxies with a fraction of 40 per cent or more of their vote in the ‘merger’ category were, in fact, true mergers.”
Galaxy Zoo 2: detailed morphological classifications for 304,122 galaxies from the Sloan Digital Sky Survey (2013, background): “Darg et al. (2010) found that a vote fraction of fmg > 0.6 robustly identified merging systems in GZ1.”
Galaxy pairs in the Sloan Digital Sky Survey – IX. Merger-induced AGN activity as traced by the Wide-field Infrared Survey Explorer (2014, methodology): “The sample of visually classified post-mergers is initiallydrawn from the Galaxy Zoo (Lintott et al. 2008) catalogue presented by Darg et al. (2010), with further visual inspection and refinement by Ellison et al. (2013).”
THE MAJOR AND MINOR GALAXY MERGER RATES AT z < 1.5 (2011, background): “Several recent studies have estimated the galaxy merger fraction and rate using large samples of visually-classified mergers at z < 1.5, including the Galaxy Zoo project (Darg et al. 2010; also Jogee et al. 2009; Bridge et al. 2010; Kartaltepe et al. 2010).”