Galaxy Zoo : Morphologies derived from visual inspection of galaxies from the Sloan Digital Sky Survey

TL;DR

Galaxy Zoo harnessed public participation to classify nearly one million galaxy images from SDSS, creating a robust morphological catalogue that surpasses proxy-based methods and enables detailed galaxy evolution studies.

Contribution

This paper introduces Galaxy Zoo, a large-scale citizen science project that provides visual galaxy classifications, demonstrating the effectiveness and reliability of public contributions in astronomical morphology.

Findings

Galaxy Zoo classifications align with professional astronomer results.

The catalogue offers unbiased morphological data avoiding proxy biases.

Color-magnitude diagrams differ significantly when using direct morphology.

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 40,000,000 individual classifications made by ~100,000 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 provides a robust morphological catalogue. Obtaining morphologies by direct visual inspection avoids introducing biases associated with proxies for morphology such as colour, concentration or structual 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.