Galaxy Zoo 2: detailed morphological classifications for 304,122
  galaxies from the Sloan Digital Sky Survey
  We present the data release for Galaxy Zoo 2 (GZ2), a citizen science project
with more than 16 million morphological classifications of 304,122 galaxies
drawn from the Sloan Digital Sky Survey. Morphology is a powerful probe for
quantifying a galaxy's dynamical history; however, automatic classifications of
morphology (either by computer analysis of images or by using other physical
parameters as proxies) still have drawbacks when compared to visual inspection.
The large number of images available in current surveys makes visual inspection
of each galaxy impractical for individual astronomers. GZ2 uses classifications
from volunteer citizen scientists to measure morphologies for all galaxies in
the DR7 Legacy survey with m_r>17, in addition to deeper images from SDSS
Stripe 82. While the original Galaxy Zoo project identified galaxies as
early-types, late-types, or mergers, GZ2 measures finer morphological features.
These include bars, bulges, and the shapes of edge-on disks, as well as
quantifying the relative strengths of galactic bulges and spiral arms. This
paper presents the full public data release for the project, including measures
of accuracy and bias. The majority (>90%) of GZ2 classifications agree with
those made by professional astronomers, especially for morphological T-types,
strong bars, and arm curvature. Both the raw and reduced data products can be
obtained in electronic format at http://data.galaxyzoo.org .
