Galaxy Zoo Builder: Morphological Dependence of Spiral Galaxy Pitch
  Angle
  Spiral structure is ubiquitous in the Universe, and the pitch angle of arms
in spiral galaxies provide an important observable in efforts to discriminate
between different mechanisms of spiral arm formation and evolution. In this
paper, we present a hierarchical Bayesian approach to galaxy pitch angle
determination, using spiral arm data obtained through the Galaxy Builder
citizen science project. We present a new approach to deal with the large
variations in pitch angle between different arms in a single galaxy, which
obtains full posterior distributions on parameters. We make use of our pitch
angles to examine previously reported links between bulge and bar strength and
pitch angle, finding no correlation in our data (with a caveat that we use
observational proxies for both bulge size and bar strength which differ from
other work). We test a recent model for spiral arm winding, which predicts
uniformity of the cotangent of pitch angle between some unknown upper and lower
limits, finding our observations are consistent with this model of transient
and recurrent spiral pitch angle as long as the pitch angle at which most
winding spirals dissipate or disappear is larger than 10 degrees.
