Galaxy Zoo: morphologies derived from visual inspection of galaxies from the Sloan Digital Sky Survey^★

Abstract

In order to understand the formation and subsequent evolution of galaxies one must first distinguish between the two main morphological classes of massive systems: spirals and early-type systems. This paper introduces a project, Galaxy Zoo, which provides visual morphological classifications for nearly one million galaxies, extracted from the Sloan Digital Sky Survey (SDSS). This achievement was made possible by inviting the general public to visually inspect and classify these galaxies via the internet. The project has obtained more than 4 × 10 7 individual classifications made by ∼10 5 participants. We discuss the motivation and strategy for this project, and detail how the classifications were performed and processed. We find that Galaxy Zoo results are consistent with those for subsets of SDSS galaxies classified by professional astronomers, thus demonstrating that our data provide a robust morphological catalogue. Obtaining morphologies by direct visual inspection avoids introducing biases associated with proxies for morphology such as colour, concentration or structural parameters. In addition, this catalogue can be used to directly compare SDSS morphologies with older data sets. The colour-magnitude diagrams for each morphological class are shown, and we illustrate how these distributions differ from those inferred using colour alone as a proxy for morphology.

Galaxy pairs in the Sloan Digital Sky Survey – VIII. The observational properties of post-merger galaxies

“…The basic Galazy Zoo sample selection includes ∼ 900,000 galaxies from the SDSS DR6, as described by Lintott et al (2008). Darg et al (2010) impose further requirements that the spectroscopic redshift of a galaxy must be 0.005 < z < 0.1 and the extinction corrected r-band Petrosian magnitude be m r < 17.77, from which they construct samples of galaxy mergers 2 .…”

Measuring the X-shaped structures in edge-on galaxies

“…At the first step we selected all edge-on galaxies from the Galaxy Zoo (Lintott et al 2008) using the following restrictions on votes: PEDGE > 0.95, PEL < 0.05, PCW < 0.05 and PACW < 0.05, which means that only objects with high probability of being edgeon galaxy and low probability of being elliptical or non edge-on disc galaxy were selected. Then, for every galaxy in our main sample with X-structures we found all edge-on galaxies with similar size (∆Rpetro < 20%), magnitude (∆mr < 0.2 mag) and redshift (∆z < 0.01).…”

J1649+2635: a grand-design spiral with a large double-lobed radio source

“…We cross-matched morphologically classified optical galaxies from Galaxy Zoo (Lintott et al 2008) with the Unified Radio Catalog (Kimball & Ivezić 2008), which contains data from both the Faint Images of the Radio Sky at Twenty-Centimeters (FIRST, Becker, White, & Helfand 1995) and the NRAO VLA Sky-Survey (NVSS, Condon et al 1998). The full Galaxy Zoo catalogue contains morphological data for 667,944 galaxies.…”