Article,
Galaxy Zoo: morphologies derived from visual inspection of galaxies from the Sloan Digital Sky Survey
Monthly Notices of the Royal Astronomical Society, 389 (3): 1179--1189 (2008)
DOI: 10.1111/j.1365-2966.2008.13689.x
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 × 107 individual classifications
made by ∼105 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.
